Looks like for some reason the package from Ubuntu (1.4) was installed instead of the one from Neon (21.04)

I'm on Slackware -current and I can confirm the same behavior from the OP.

Operating System: Slackware 14.2+ (aka -current)
KDE Plasma Version: 5.22.1
KDE Frameworks Version: 5.83.0
Qt Version: 5.15.2
Kernel Version: 5.12.11 (64-bit)
Graphics Platform: X11

Error report (missing some debug symbols):

[KCrash Handler]
#4  0x00007f9449c98668 in Device::reloadPlugins() () from /usr/lib64/libkdeconnectcore.so.21
#5  0x00007f9449c99908 in Device::addLink(NetworkPacket const&, DeviceLink*) () from /usr/lib64/libkdeconnectcore.so.21
#6  0x00007f9449c92424 in Daemon::onNewDeviceLink(NetworkPacket const&, DeviceLink*) () from /usr/lib64/libkdeconnectcore.so.21
#7  0x00007f944811baf4 in ?? () from /usr/lib64/libQt5Core.so.5
#8  0x00007f9449c68c64 in LinkProvider::onConnectionReceived(NetworkPacket const&, DeviceLink*) () from /usr/lib64/libkdeconnectcore.so.21
#9  0x00007f9449c73f67 in LanLinkProvider::encrypted() () from /usr/lib64/libkdeconnectcore.so.21
#10 0x00007f944811baf4 in ?? () from /usr/lib64/libQt5Core.so.5
#11 0x00007f94497360af in ?? () from /usr/lib64/libQt5Network.so.5
#12 0x00007f944973c51b in ?? () from /usr/lib64/libQt5Network.so.5
#13 0x00007f944973cb86 in ?? () from /usr/lib64/libQt5Network.so.5
#14 0x00007f944811bb28 in ?? () from /usr/lib64/libQt5Core.so.5
#15 0x00007f94496fb2ff in ?? () from /usr/lib64/libQt5Network.so.5
#16 0x00007f944970cdc1 in ?? () from /usr/lib64/libQt5Network.so.5
#17 0x00007f9448d12a8f in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#18 0x00007f94480e719a in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib64/libQt5Core.so.5
#19 0x00007f944813c195 in ?? () from /usr/lib64/libQt5Core.so.5
#20 0x00007f9444c6ff9b in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#21 0x00007f9444c70218 in ?? () from /usr/lib64/libglib-2.0.so.0
#22 0x00007f9444c702bf in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#23 0x00007f944813b67b in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#24 0x00007f94480e5d4b in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#25 0x00007f94480ed93c in QCoreApplication::exec() () from /usr/lib64/libQt5Core.so.5
#26 0x0000000000404a49 in ?? ()
#27 0x00007f944793f1ad in __libc_start_main () from /lib64/libc.so.6
#28 0x0000000000404d1a in _start ()
[Inferior 1 (process 2494) detached]

What I did:

- Installing kdeconnect 21.04.02 in Synaptic Package Manager
- Lock Version in "Package -> Lock Version"
- With every announced update the package "kdeconnect 21.04.02" still is replaced with "kdeconnect 1.4" 
- consequence: kdeconnect crashes again

What is to do?

(In reply to Deny Dias from comment #2)
> I'm on Slackware -current and I can confirm the same behavior from the OP.
> 

judging by the backtrace this looks like https://bugs.kde.org/show_bug.cgi?id=438065, although you're the first non-Neon user to report that

(In reply to Nicolas Fella from comment #4)
> judging by the backtrace this looks like
> https://bugs.kde.org/show_bug.cgi?id=438065, although you're the first
> non-Neon user to report that

Yeap, it does. At least one Slackware user (besides me) can confirm the bug here (Slackware room at matrix.org):

https://matrix.to/#/!txOpDzDRbZXoMPztLz:matrix.org/$1623895287494382rXnci:matrix.org

Please run killall kdeconnectd and 'QT_LOGGING_RULES="*kdeconnect*=true" /usr/lib/libexec/kdeconnectd' (exact path may vary), reproduce the crash and show the output here

(In reply to Nicolas Fella from comment #6)
> Please run killall kdeconnectd and 'QT_LOGGING_RULES="*kdeconnect*=true"
> /usr/lib/libexec/kdeconnectd' (exact path may vary), reproduce the crash and
> show the output here

Done. The daemon path is different in Slackware.

kdeconnect.core: Daemon starting
kdeconnect.core: LanLinkProvider started
kdeconnect.core: Daemon started
kdeconnect.core: Broadcasting identity packet
kdeconnect.core: TCP connection done (i'm the existing device)
kdeconnect.core: Starting server ssl (I'm the client TCP socket)
kdeconnect.core: Socket successfully established an SSL connection
kdeconnect.core: It is a known device "MobileDevice"
kdeconnect.core: Not loading plugin "kdeconnect_remotesystemvolume" because device doesn't support it
kdeconnect.core: Not loading plugin "kdeconnect_lockdevice" because device doesn't support it
kdeconnect.core: Not loading plugin "kdeconnect_remotecommands" because device doesn't support it
kdeconnect.core: KPluginFactory could not load the plugin: "kdeconnect_findthisdevice" "Cannot load library /usr/lib64/qt5/plugins/kdeconnect/kdeconnect_findthisdevice.so: (libKF5PulseAudioQt.so.2: cannot open shared object file: No such file or directory)"
kdeconnect.core: KPluginFactory could not load the plugin: "kdeconnect_pausemusic" "Cannot load library /usr/lib64/qt5/plugins/kdeconnect/kdeconnect_pausemusic.so: (libKF5PulseAudioQt.so.2: cannot open shared object file: No such file or directory)"
kdeconnect.plugin.sftp: add to dolphin
kdeconnect.plugin.sftp: Created device: "MobileDevice"
Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
kdeconnect.plugin.mpris: MPRIS service "org.mpris.MediaPlayer2.chromium.instance4563" just came online
kdeconnect.plugin.mpris: Mpris addPlayer "org.mpris.MediaPlayer2.chromium.instance4563" -> "Vivaldi"
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kdeconnectd path = /usr/lib64 pid = 26046
KCrash: Arguments: /usr/lib64/kdeconnectd
KCrash: Attempting to start /usr/lib64/drkonqi
QSocketNotifier: Invalid socket 8 and type 'Read', disabling...
QSocketNotifier: Invalid socket 10 and type 'Read', disabling...
QSocketNotifier: Invalid socket 11 and type 'Read', disabling...
QSocketNotifier: Invalid socket 12 and type 'Read', disabling...

Seems like we have to sort some plugin paths in Slackware...

> "Cannot load library /usr/lib64/qt5/plugins/kdeconnect/kdeconnect_pausemusic.so: (libKF5PulseAudioQt.so.2: cannot open shared object file: No such file or directory)"

pulseaudio-qt was updated recently and broke ABI. Please ask the package maintainer to rebuild kdeconnect

(In reply to Nicolas Fella from comment #8)
> pulseaudio-qt was updated recently and broke ABI. Please ask the package
> maintainer to rebuild kdeconnect

Sure thing! Thanks for the help.

A Slackware64-current user here. Found this bug report looking for issues with KDE Connect. Constant aborts when trying to load kdeconnect, output from Deny Dias looks similar not going to repeat it here.

My point in posting is Slackware64-current from the ChangeLog.txt the package pulseaudio-qt-1.3 was upgraded on June 14, the package kdeconnect-kde-21.04.2 was last upgraded on June 10.

So I rebuilt kdeconnect-kde-21.04.2 on this system against the upgraded version of pulseaudio-qt-1.3 and this does indeed fix all issues as far as I can tell. I have two devices connected all that I've tested works.

Operating System: Slackware -current
KDE Plasma Version: 5.22.1
KDE Frameworks Version: 5.83.0
Qt Version: 5.15.2
Kernel Version: 5.12.10 (64-bit)

(In reply to Chris from comment #10)
> rebuilt kdeconnect-kde-21.04.2 on this system against the upgraded
> version of pulseaudio-qt-1.3 and this does indeed fix all issues as far as I
> can tell.

I reported this on LQ so PV could bump pulseaudio-qt-1.3. Thanks for the note tho.

(In reply to Deny Dias from comment #11)
> (In reply to Chris from comment #10)
> > rebuilt kdeconnect-kde-21.04.2 on this system against the upgraded
> > version of pulseaudio-qt-1.3 and this does indeed fix all issues as far as I
> > can tell.
> 
> I reported this on LQ so PV could bump pulseaudio-qt-1.3. Thanks for the
> note tho.

I noted your post on the forum and replied to it.

(In reply to Chris from comment #12)
> I noted your post on the forum and replied to it.

Oh! I see. Well, kdeconnect-kde-21.04.2-x86_64-2 was compiled against newer pulseaudio-qt-1.3-x86_64-1. Everything looks fine now on slackland.

Created attachment 161094 [details]
New crash information added by DrKonqi

kdeconnectd (23.04.3) using Qt 5.15.10

Happens to me on almost every single boot. Regardless of how many times I try to restart the kdeconnect deamon, the issue persists. Sometimes a reboot fixes it.

-- Backtrace (Reduced):
#4  0x00007f328a180fa4 in Device::reloadPlugins() () at /usr/lib/libkdeconnectcore.so.23
#5  0x00007f328a182040 in Device::addLink(NetworkPacket const&, DeviceLink*) () at /usr/lib/libkdeconnectcore.so.23
#6  0x00007f328a17b333 in Daemon::onNewDeviceLink(NetworkPacket const&, DeviceLink*) () at /usr/lib/libkdeconnectcore.so.23
[...]
#8  0x00007f328a15b739 in LinkProvider::onConnectionReceived(NetworkPacket const&, DeviceLink*) () at /usr/lib/libkdeconnectcore.so.23
#9  0x00007f328a16779f in LanLinkProvider::encrypted() () at /usr/lib/libkdeconnectcore.so.23

I have this crash occurring frequently, after a Neon testing update a few days ago. 

This is the backtrace:

#0  __pthread_kill_implementation (no_tid=0, signo=11, threadid=<optimized out>) at ./nptl/pthread_kill.c:44
#1  __pthread_kill_internal (signo=11, threadid=<optimized out>) at ./nptl/pthread_kill.c:78
#2  __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=11) at ./nptl/pthread_kill.c:89
#3  0x00007faf25242866 in __GI_raise (sig=11) at ../sysdeps/posix/raise.c:26
#4  0x00007faf267070cd in KCrash::defaultCrashHandler(int) () from /lib/x86_64-linux-gnu/libKF5Crash.so.5
#5  <signal handler called>
#6  Device::reloadPlugins (this=this@entry=0x5565731fcfd0) at ./core/device.cpp:184
#7  0x00007faf274a1591 in Device::addLink (this=0x5565731fcfd0, link=<optimized out>) at ./core/device.cpp:292
#8  0x00007faf2749c3a1 in Daemon::onNewDeviceLink (this=0x7ffc614e1aa0, link=0x5565732e3980) at ./core/daemon.cpp:170
#9  0x00007faf25cf4924 in QtPrivate::QSlotObjectBase::call (a=0x7ffc614e0110, r=0x7ffc614e1aa0, this=0x55657323ef60) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#10 doActivate<false> (sender=0x556573131a20, signal_index=3, argv=0x7ffc614e0110) at kernel/qobject.cpp:3925
#11 0x00007faf25ced9f7 in QMetaObject::activate (sender=sender@entry=0x556573131a20, m=m@entry=0x7faf274b37e0 <LinkProvider::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7ffc614e0110)
    at kernel/qobject.cpp:3985
#12 0x00007faf2747b903 in LinkProvider::onConnectionReceived (this=this@entry=0x556573131a20, _t1=<optimized out>, _t1@entry=0x5565732e3980) at ./obj-x86_64-linux-gnu/core/kdeconnectcore_autogen/CSWKE6ESUK/moc_linkprovider.cpp:178
#13 0x00007faf274867c4 in LanLinkProvider::addLink (this=this@entry=0x556573131a20, socket=<optimized out>, deviceInfo=...) at ./core/backends/lan/lanlinkprovider.cpp:614
#14 0x00007faf274873cf in LanLinkProvider::encrypted (this=0x556573131a20) at ./core/backends/lan/lanlinkprovider.cpp:377
#15 0x00007faf25cf4924 in QtPrivate::QSlotObjectBase::call (a=0x7ffc614e0410, r=0x556573131a20, this=0x5565732b24a0) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#16 doActivate<false> (sender=0x556572f71c50, signal_index=16, argv=0x7ffc614e0410) at kernel/qobject.cpp:3925
#17 0x00007faf25ced9f7 in QMetaObject::activate (sender=sender@entry=0x556572f71c50, m=m@entry=0x7faf251fa0e0 <QSslSocket::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x0)
    at kernel/qobject.cpp:3985
#18 0x00007faf25164604 in QSslSocket::encrypted (this=this@entry=0x556572f71c50) at .moc/moc_qsslsocket.cpp:317
#19 0x00007faf251847d3 in QSslSocketBackendPrivate::continueHandshake (this=0x55657312c350) at ssl/qsslsocket_openssl.cpp:2045
#20 0x00007faf2518b13b in QSslSocketBackendPrivate::startHandshake (this=this@entry=0x55657312c350) at ssl/qsslsocket_openssl.cpp:1480
#21 0x00007faf2518b903 in QSslSocketBackendPrivate::transmit (this=0x55657312c350) at ssl/qsslsocket_openssl.cpp:1136
#22 0x00007faf25cf4958 in doActivate<false> (sender=0x5565732bcc00, signal_index=3, argv=0x7ffc614e1670) at kernel/qobject.cpp:3937
#23 0x00007faf25ced9f7 in QMetaObject::activate (sender=sender@entry=0x5565732bcc00, m=m@entry=0x7faf25f5a960 <QIODevice::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x0) at kernel/qobject.cpp:3985
#24 0x00007faf25be7394 in QIODevice::readyRead (this=this@entry=0x5565732bcc00) at .moc/moc_qiodevice.cpp:190
#25 0x00007faf2513a21f in QAbstractSocketPrivate::emitReadyRead (channel=0, this=0x556573027620) at socket/qabstractsocket.cpp:1323
#26 QAbstractSocketPrivate::canReadNotification (this=0x556573027620) at socket/qabstractsocket.cpp:748
#27 0x00007faf2514d359 in QReadNotifier::event (this=<optimized out>, e=<optimized out>) at socket/qnativesocketengine.cpp:1274
#28 0x00007faf2696c763 in QApplicationPrivate::notify_helper (this=<optimized out>, receiver=0x55657327c390, e=0x7ffc614e17b0) at kernel/qapplication.cpp:3640
#29 0x00007faf25cbce7a in QCoreApplication::notifyInternal2 (receiver=0x55657327c390, event=0x7ffc614e17b0) at kernel/qcoreapplication.cpp:1064
#30 0x00007faf25cbd052 in QCoreApplication::sendEvent (receiver=<optimized out>, event=<optimized out>) at kernel/qcoreapplication.cpp:1462
#31 0x00007faf25d16f75 in socketNotifierSourceDispatch (source=0x556572fab550) at kernel/qeventdispatcher_glib.cpp:107
#32 0x00007faf2471949d in g_main_dispatch (context=0x7faf1c000ee0) at ../../../glib/gmain.c:3460
#33 g_main_context_dispatch (context=0x7faf1c000ee0) at ../../../glib/gmain.c:4200
#34 0x00007faf24774178 in g_main_context_iterate.constprop.0 (context=0x7faf1c000ee0, block=<optimized out>, dispatch=1, self=<optimized out>) at ../../../glib/gmain.c:4276
#35 0x00007faf247181b0 in g_main_context_iteration (context=0x7faf1c000ee0, may_block=1) at ../../../glib/gmain.c:4343
#36 0x00007faf25d163de in QEventDispatcherGlib::processEvents (this=0x556572fab430, flags=...) at kernel/qeventdispatcher_glib.cpp:425
#37 0x00007faf25cbb79b in QEventLoop::exec (this=this@entry=0x7ffc614e19c0, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#38 0x00007faf25cc3d44 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#39 0x00007faf26136d50 in QGuiApplication::exec () at kernel/qguiapplication.cpp:1863
#40 0x00007faf2696c6d9 in QApplication::exec () at kernel/qapplication.cpp:2832
#41 0x0000556571714001 in main (argc=<optimized out>, argv=<optimized out>) at ./daemon/kdeconnectd.cpp:186

I don't know if it matters, but I'm using Pipewire instead of PulseAudio and a plasma-pa built from upstream sources that allows relying on pipewire-pulse.

Also, this backtrace looks like the bug traces for: bug #474993, bug #438066, bug #438065, bug #438064, bug #438062, bug #438060

*** This bug has been marked as a duplicate of bug 475054 ***