SUMMARY

I was using Plasma 5.20.90 on Wayland in Fedora Rawhide/34. I started System Settings and selected Appearance > Global Theme. I switched the Global theme to Breeze and pressed Apply. I switched the Global theme to Fedora and pressed Apply. plasmashell aborted with the error message "The Wayland connection experienced a fatal error: Invalid argument" The screen went black. plasmashell didn't restart automatically. plasmashell aborted 4 of 5 times I changed the Global theme to Fedora in Plasma 5.20.90 on Wayland. The journal showed the following at the time of the last crash which had the same types of errors as the others.

Feb 03 22:31:43 systemsettings5[11115]: QDBusConnection: error: could not send signal to service "" path "//home/matt/.kde/share/config/kdeglobals" interface "org.kde.kconfig.notify" member "ConfigChanged": Invalid object path: //home/matt/.kde/share/config/kdeglobals
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:406:376: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:407:130: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:408:130: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:408:393: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:409:130: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:410:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:411:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:412:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:413:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:413:379: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:43 plasmashell[9277]: qt.svg: <input>:413:631: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 systemsettings5[11115]: QDBusConnection: error: could not send signal to service "" path "//home/matt/.kde/share/config/kdeglobals" interface "org.kde.kconfig.notify" member "ConfigChanged": Invalid object path: //home/matt/.kde/share/config/kdeglobals
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:406:376: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:407:130: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:408:130: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:408:393: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:409:130: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:410:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:411:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:412:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:413:129: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:413:379: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:49 plasmashell[9277]: qt.svg: <input>:413:631: Could not add child element to parent element because the types are incorrect.
Feb 03 22:31:58 systemsettings5[11115]: QDBusConnection: error: could not send signal to service "" path "//home/matt/.kde/share/config/kdeglobals" interface "org.kde.kconfig.notify" member "ConfigChanged": Invalid object path: //home/matt/.kde/share/config/kdeglobals
Feb 03 22:31:58 plasmashell[9277]: wl_display@1: error 0: invalid object 390
Feb 03 22:31:58 plasmashell[9277]: The Wayland connection experienced a fatal error: Invalid argument
Feb 03 22:32:07 systemsettings5[11115]: QDBusConnection: error: could not send signal to service "" path "//home/matt/.kde/share/config/kdeglobals" interface "org.kde.kconfig.notify" member "ConfigChanged": Invalid object path: //home/matt/.kde/share/config/kdeglobals
Feb 03 22:34:50 systemd[1]: Started dbus-:1.8-org.kde.powerdevil.backlighthelper@9.service.
Feb 03 22:34:50 audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=dbus-:1.8-org.kde.powerdevil.backlighthelper@9 comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Feb 03 22:35:00 systemd[1]: dbus-:1.8-org.kde.powerdevil.backlighthelper@9.service: Succeeded.
Feb 03 22:35:00 audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=dbus-:1.8-org.kde.powerdevil.backlighthelper@9 comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Feb 03 22:36:05 systemd[1]: Started dbus-:1.8-org.kde.powerdevil.backlighthelper@10.service.
Feb 03 22:36:05 audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=dbus-:1.8-org.kde.powerdevil.backlighthelper@10 comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Feb 03 22:36:15 systemd[1]: dbus-:1.8-org.kde.powerdevil.backlighthelper@10.service: Succeeded.
Feb 03 22:36:15 audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=dbus-:1.8-org.kde.powerdevil.backlighthelper@10 comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Feb 03 22:36:36 plasmashell[9277]: KCrash: Application 'plasmashell' crashing...
Feb 03 22:36:36 plasmashell[9277]: KCrash: Attempting to start /usr/libexec/drkonqi
Feb 03 22:36:37 systemd[9112]: plasma-plasmashell.service: Succeeded.
Feb 03 22:36:37 systemd[9112]: plasma-plasmashell.service: Consumed 28.107s CPU time.

drkonqi crashed when trying to analyze the plasmashell crash each time. I switched to another VT and ran gdb -p 9277 (plasmashell's pid). I switched back to Plasma and changed the Global theme to Fedora as above. The trace of the crashing thread 1 was as follows.

Core was generated by `/usr/bin/plasmashell'.
Program terminated with signal SIGABRT, Aborted.
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:49
49        return ret;
[Current thread is 1 (Thread 0x7fc5ea90d940 (LWP 9277))]

(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:49
#1  0x00007fc5e910e8a4 in __GI_abort () at abort.c:79
#2  0x00007fc5e958942d in qt_message_fatal (message=<synthetic pointer>..., context=...)
    at global/qlogging.cpp:1914
#3  QMessageLogger::fatal(char const*, ...) const
    (this=this@entry=0x7ffdde149100, msg=msg@entry=0x7fc5e745ccf8 "The Wayland connection experienced a fatal error: %s") at global/qlogging.cpp:893
#4  0x00007fc5e73e04e4 in QtWaylandClient::QWaylandDisplay::checkError() const (this=<optimized out>)
    at /usr/src/debug/qt5-qtwayland-5.15.2-4.fc34.x86_64/src/client/qwaylanddisplay.cpp:211
#5  0x00007fc5e73e06fa in QtWaylandClient::QWaylandDisplay::flushRequests() (this=0x55bc3367a8b0)
    at /usr/src/debug/qt5-qtwayland-5.15.2-4.fc34.x86_64/src/client/qwaylanddisplay.cpp:222
#6  0x00007fc5e97874cd in doActivate<false>(QObject*, int, void**)
    (sender=0x55bc336b73e0, signal_index=4, argv=0x7ffdde149200) at kernel/qobject.cpp:3898
#7  0x00007fc5e97819b7 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**)
    (sender=sender@entry=0x55bc336b73e0, m=m@entry=0x7fc5e9a1bac0 <QAbstractEventDispatcher::staticMetaObject>, local_signal_index=local_signal_index@entry=1, argv=argv@entry=0x0)
    at kernel/qobject.cpp:3946
#8  0x00007fc5e9753a57 in QAbstractEventDispatcher::awake() (this=this@entry=0x55bc336b73e0)
    at .moc/moc_qabstracteventdispatcher.cpp:149
#9  0x00007fc5e97a375b in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)
    (this=0x55bc336b73e0, flags=...) at kernel/qeventdispatcher_glib.cpp:430
#10 0x00007fc5e9755982 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)
    (this=this@entry=0x7ffdde149320, flags=..., flags@entry=...)
    at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#11 0x00007fc5e975d514 in QCoreApplication::exec() ()
--Type <RET> for more, q to quit, c to continue without paging--c
    at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#12 0x000055bc3300e756 in main(int, char**) (argc=<optimized out>, argv=0x7ffdde149530) at /usr/src/debug/plasma-workspace-5.20.90-9.fc34.x86_64/shell/main.cpp:247


STEPS TO REPRODUCE
1. Boot a Fedora Rawhide/34 KDE Plasma spin updated to 2020-2-3
2. Log in to Plasma 5.20.90 on Wayland
3. Start System Settings
4. Select Appearance > Global Theme
5. Change the Global theme to Breeze and click Apply
6. Change the Global theme to Fedora and click Apply
7. If the crash didn't happen, repeat 5-6 until it does

OBSERVED RESULT
plasmashell on Wayland aborted when changing Global Theme to Fedora in System settings

EXPECTED RESULT
No crash would happen and the Global theme would be changed normally.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora Rawhide/34
(available in About System)
KDE Plasma Version: 5.19.90
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
I reported plasmashell crashed with the error message "The Wayland connection experienced a fatal error: Invalid argument" when logging in at https://bugs.kde.org/show_bug.cgi?id=424879 I made this a different report since the crashes happened in different ways and with different versions so I'm unsure if they were related.