SUMMARY
No reproducing behavior I'm aware of. Happened 4 times in 2 days on master.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.25
(available in About System)
KDE Plasma Version: 5.25.4
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.5

#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x00007efc13377859 in __GI_abort () at abort.c:79
#2  0x00007efc13a27bd9 in  () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007efc13a26fe5 in qt_assert_x(char const*, char const*, char const*, int) ()
    at /lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x000055ad3d79560d in KWin::ScreenCastStream::onStreamAddBuffer(void*, pw_buffer*)
    (data=0x55ad3f3752b0, buffer=0x55ad3f344598)
    at /home/eric/kde/src/kwin/src/plugins/screencast/screencaststream.cpp:196
#5  0x00007efc139323fb in  () at /lib/x86_64-linux-gnu/libpipewire-0.3.so.0
#6  0x00007efc1392b1a5 in pw_impl_port_use_buffers () at /lib/x86_64-linux-gnu/libpipewire-0.3.so.0
#7  0x00007efbfa86af4c in  () at /usr/lib/x86_64-linux-gnu/pipewire-0.3/libpipewire-module-client-node.so
#8  0x00007efbfa87d8bf in  () at /usr/lib/x86_64-linux-gnu/pipewire-0.3/libpipewire-module-client-node.so
#9  0x00007efbfa8e4cda in  () at /usr/lib/x86_64-linux-gnu/pipewire-0.3/libpipewire-module-protocol-native.so
#10 0x00007efbfa8e5230 in  () at /usr/lib/x86_64-linux-gnu/pipewire-0.3/libpipewire-module-protocol-native.so
#11 0x00007efbfaed5783 in  () at /usr/lib/x86_64-linux-gnu/spa-0.2/support/libspa-support.so
#12 0x000055ad3d788d2b in operator()() const (__closure=0x55ad3ec9fbb0)
    at /home/eric/kde/src/kwin/src/plugins/screencast/pipewirecore.cpp:69
#13 0x000055ad3d7897df in QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, KWin::PipeWireCore::init()::<lambda()> >::call(struct {...} &, void **) (f=..., arg=0x7ffea2643b10)
    at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:146
#14 0x000055ad3d7897b1 in QtPrivate::Functor<KWin::PipeWireCore::init()::<lambda()>, 0>::call<QtPrivate::List<>, void>(struct {...} &, void *, void **) (f=..., arg=0x7ffea2643b10)
    at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:256
#15 0x000055ad3d789780 in QtPrivate::QFunctorSlotObject<KWin::PipeWireCore::init()::<lambda()>, 0, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void **, bool *)
    (which=1, this_=0x55ad3ec9fba0, r=0x55ad3dde5910, a=0x7ffea2643b10, ret=0x0)
    at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:443
#16 0x00007efc13c80d1e in  () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#17 0x00007efc13c84df3 in QSocketNotifier::activated(QSocketDescriptor, QSocketNotifier::Type, QSocketNotifier::QPrivateSignal) () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#18 0x00007efc13c85593 in QSocketNotifier::event(QEvent*) () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#19 0x00007efc14a1fe83 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
    at /lib/x86_64-linux-gnu/libQt5Widgets.so.5
#20 0x00007efc14a28c98 in QApplication::notify(QObject*, QEvent*) () at /lib/x86_64-linux-gnu/libQt5Widgets.so.5
#21 0x00007efc13c49c6a in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
    at /lib/x86_64-linux-gnu/libQt5Core.so.5
#22 0x00007efc13ca17cb in QEventDispatcherUNIXPrivate::activateSocketNotifiers() ()
    at /lib/x86_64-linux-gnu/libQt5Core.so.5
#23 0x00007efc13ca1c2b in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
--Type <RET> for more, q to quit, c to continue without paging--c
    at /lib/x86_64-linux-gnu/libQt5Core.so.5
#24 0x000055ad3d8b4dd1 in QUnixEventDispatcherQPA::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
#25 0x00007efc13c4876b in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#26 0x00007efc13c50914 in QCoreApplication::exec() () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#27 0x000055ad3d73d96f in main(int, char**) (argc=14, argv=0x7ffea2644388) at /home/eric/kde/src/kwin/src/main_wayland.cpp:620