Could you add debug symbols for kate, KTextEditor, Qt, and uim and reproduce again?
Could you then also run kate with: valgrind kate

And oaste the output here?

Here is a complete backtrace, sorry for the incomplete one...

$ gdb kate
GNU gdb (Debian 8.3.1-1) 8.3.1
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from kate...
Reading symbols from /usr/lib/debug/.build-id/40/0ef647fb83779c28de741677bca09928f540ab.debug...
(gdb) r
Starting program: /usr/bin/kate 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
QSocketNotifier: Can only be used with threads started with QThread
qt5ct: using qt5ct plugin
[New Thread 0x7ffff031d700 (LWP 32629)]
qt5ct: D-Bus global menu: no
Hspell: can't open /usr/share/hspell/hebrew.wgz.sizes.
sonnet.plugins.hspell: HSpellDict::HSpellDict: Init failed
Using Wayland-EGL
[New Thread 0x7fffe7347700 (LWP 32632)]
Using the 'xdg-shell' shell integration
qt.qpa.wayland: Wayland does not support QWindow::requestActivate()
qt5ct: palette support is disabled
[Detaching after fork from child process 32641]

Thread 1 "kate" received signal SIGSEGV, Segmentation fault.
QCoreApplication::notifyInternal2 (receiver=0x0, event=0x7fffffffd430) at kernel/qcoreapplication.cpp:1083
1083    kernel/qcoreapplication.cpp: Aucun fichier ou dossier de ce type.
(gdb) thread apply all bt

Thread 3 (Thread 0x7fffe7347700 (LWP 32632)):
#0  futex_wait_cancelable (private=0, expected=0, futex_word=0x55555585c7b8) at ../sysdeps/unix/sysv/linux/futex-internal.h:88
#1  __pthread_cond_wait_common (abstime=0x0, mutex=0x55555585c768, cond=0x55555585c790) at pthread_cond_wait.c:502
#2  __pthread_cond_wait (cond=0x55555585c790, mutex=0x55555585c768) at pthread_cond_wait.c:655
#3  0x00007fffe782330b in cnd_wait (mtx=0x55555585c768, cond=0x55555585c790) at ../include/c11/threads_posix.h:155
#4  util_queue_thread_func (input=input@entry=0x555556061ea0) at ../src/util/u_queue.c:272
#5  0x00007fffe7822f27 in impl_thrd_routine (p=<optimized out>) at ../include/c11/threads_posix.h:87
#6  0x00007ffff4863fb7 in start_thread (arg=<optimized out>) at pthread_create.c:486
#7  0x00007ffff5cab2cf in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 2 (Thread 0x7ffff031d700 (LWP 32629)):
#0  0x00007ffff5ca0d0f in __GI___poll (fds=0x7fffe8005260, nfds=2, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007ffff3ff309e in g_main_context_poll (priority=<optimized out>, n_fds=2, fds=0x7fffe8005260, timeout=<optimized out>, context=0x7fffe8000bf0) at ../../../glib/gmain.c:4216
#2  g_main_context_iterate (context=context@entry=0x7fffe8000bf0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:3912
#3  0x00007ffff3ff31bf in g_main_context_iteration (context=0x7fffe8000bf0, may_block=may_block@entry=1) at ../../../glib/gmain.c:3978
#4  0x00007ffff621e7f1 in QEventDispatcherGlib::processEvents (this=0x7fffe8000b20, flags=...) at kernel/qeventdispatcher_glib.cpp:422
#5  0x00007ffff61c771b in QEventLoop::exec (this=this@entry=0x7ffff031cd30, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:140
#6  0x00007ffff6008751 in QThread::exec (this=this@entry=0x7ffff651cd80 <(anonymous namespace)::Q_QGS__q_manager::innerFunction()::holder>) at ../../include/QtCore/../../src/corelib/global/qflags.h:120
#7  0x00007ffff649b4e6 in QDBusConnectionManager::run (this=0x7ffff651cd80 <(anonymous namespace)::Q_QGS__q_manager::innerFunction()::holder>) at qdbusconnection.cpp:178
#8  0x00007ffff60098d2 in QThreadPrivate::start (arg=0x7ffff651cd80 <(anonymous namespace)::Q_QGS__q_manager::innerFunction()::holder>) at thread/qthread_unix.cpp:361
#9  0x00007ffff4863fb7 in start_thread (arg=<optimized out>) at pthread_create.c:486
#10 0x00007ffff5cab2cf in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 1 (Thread 0x7ffff1843840 (LWP 32584)):
#0  QCoreApplication::notifyInternal2 (receiver=0x0, event=0x7fffffffd430) at kernel/qcoreapplication.cpp:1083
#1  0x00007ffff1441174 in QUimPlatformInputContext::updatePreedit() () from /usr/lib/x86_64-linux-gnu/qt5/plugins/platforminputcontexts/libuimplatforminputcontextplugin.so
#2  0x00007ffff12303f8 in im_update_preedit (uc_=<optimized out>) at uim-func.c:130
#3  0x00007ffff1206d0c in call (proc=<optimized out>, args=30, eval_state=0x7fffffffd560, need_eval=SCM_VALTYPE_NEED_EVAL) at ../sigscheme/src/eval.c:415
#4  0x00007ffff1206f79 in scm_eval (obj=<optimized out>, env=<optimized out>, env@entry=93825007257264) at ../sigscheme/src/eval.c:499
#5  0x00007ffff1211c36 in scm_s_letstar (bindings=30, body=140737237855536, eval_state=0x7fffffffd6a0) at ../sigscheme/src/syntax.c:611
#6  0x00007ffff1206cdb in call (proc=<optimized out>, args=140737237855536, eval_state=0x7fffffffd6a0, need_eval=SCM_VALTYPE_AS_IS) at ../sigscheme/src/eval.c:420
#7  0x00007ffff1206f79 in scm_eval (obj=<optimized out>, env=<optimized out>, env@entry=93825007260032) at ../sigscheme/src/eval.c:499
#8  0x00007ffff12070b1 in scm_s_begin (args=140737237856912, args@entry=140737237856032, eval_state=eval_state@entry=0x7fffffffd810) at ../sigscheme/src/syntax.c:830
#9  0x00007ffff1207219 in scm_s_body (body=140737237856032, eval_state=0x7fffffffd810) at ../sigscheme/src/syntax.c:799
#10 0x00007ffff1206cdb in call (proc=<optimized out>, args=140737237856032, eval_state=0x7fffffffd810, need_eval=SCM_VALTYPE_AS_IS) at ../sigscheme/src/eval.c:420
#11 0x00007ffff1206f79 in scm_eval (obj=<optimized out>, env=<optimized out>) at ../sigscheme/src/eval.c:499
#12 0x00007ffff12075a4 in scm_call (proc=<optimized out>, args=<optimized out>) at ../sigscheme/src/eval.c:94
#13 0x00007ffff142c2fd in GCROOTS_call_with_gc_ready_stack (ctx=0x555555654370, proc=proc@entry=0x7ffff12163c0 <uim_scm_callf_internal>, arg=arg@entry=0x7fffffffd8b8) at gcroots.c:114
#14 0x00007ffff12159f2 in scm_call_with_gc_ready_stack (arg=0x7fffffffd8b8, func=func@entry=0x7ffff12163c0 <uim_scm_callf_internal>) at ../sigscheme/src/storage-gc.c:376
#15 uim_scm_call_with_gc_ready_stack (func=func@entry=0x7ffff12163c0 <uim_scm_callf_internal>, arg=arg@entry=0x7fffffffd8c0) at uim-scm-sigscheme.c:458
#16 0x00007ffff12168c3 in uim_scm_callf (proc=proc@entry=0x7ffff1235352 "key-press-handler", args_fmt=args_fmt@entry=0x7ffff1235378 "poi") at uim-scm-sigscheme.c:1010
#17 0x00007ffff122fefd in filter_key (uc=uc@entry=0x555555654390, key=key@entry=32, state=state@entry=0, is_press=is_press@entry=1) at uim-key.c:368
#18 0x00007ffff122fff0 in filter_key (is_press=1, state=0, key=32, uc=0x555555654390) at uim-key.c:352
#19 uim_press_key (uc=0x555555654390, key=32, state=0) at uim-key.c:395
#20 0x00007ffff143f7fe in QUimPlatformInputContext::filterEvent(QEvent const*) () from /usr/lib/x86_64-linux-gnu/qt5/plugins/platforminputcontexts/libuimplatforminputcontextplugin.so
#21 0x00007ffff137f8bd in QtWaylandClient::sendKey (tlw=0x555556045250, timestamp=timestamp@entry=7527518, type=type@entry=QEvent::KeyPress, key=key@entry=32, modifiers=..., nativeScanCode=nativeScanCode@entry=65, nativeVirtualKey=32, nativeModifiers=0, text=..., autorep=false, count=1) at qwaylandinputdevice.cpp:715
#22 0x00007ffff137fc2b in QtWaylandClient::QWaylandInputDevice::Keyboard::keyboard_key (this=0x555555651d30, serial=<optimized out>, time=7527518, key=57, state=1) at qwaylandinputdevice.cpp:779
#23 0x00007ffff7fad8ee in ffi_call_unix64 () at ../src/x86/unix64.S:76
#24 0x00007ffff7fad2bf in ffi_call (cif=cif@entry=0x7fffffffdd20, fn=<optimized out>, rvalue=<optimized out>, rvalue@entry=0x0, avalue=avalue@entry=0x7fffffffddf0) at ../src/x86/ffi64.c:525
#25 0x00007ffff7fba30d in wl_closure_invoke (closure=closure@entry=0x555555c68610, flags=flags@entry=1, target=<optimized out>, target@entry=0x5555556545b0, opcode=opcode@entry=3, data=<optimized out>) at ../src/connection.c:1014
#26 0x00007ffff7fb6ac9 in dispatch_event (display=display@entry=0x5555556492d0, queue=<optimized out>) at ../src/wayland-client.c:1430
#27 0x00007ffff7fb7fc4 in dispatch_queue (queue=0x555555649398, display=0x5555556492d0) at ../src/wayland-client.c:1576
#28 wl_display_dispatch_queue_pending (display=0x5555556492d0, queue=0x555555649398) at ../src/wayland-client.c:1818
#29 0x00007ffff7fb801c in wl_display_dispatch_pending (display=<optimized out>) at ../src/wayland-client.c:1881
#30 0x00007ffff13809b2 in QtWaylandClient::QWaylandDisplay::flushRequests (this=0x5555556437e0) at qwaylanddisplay.cpp:187
#31 0x00007ffff61f33c8 in QMetaObject::activate (sender=0x555555685870, signalOffset=<optimized out>, local_signal_index=<optimized out>, argv=<optimized out>) at kernel/qobject.cpp:3803
#32 0x00007ffff621e82f in QEventDispatcherGlib::processEvents (this=0x555555685870, flags=...) at kernel/qeventdispatcher_glib.cpp:429
#33 0x00007ffff61c771b in QEventLoop::exec (this=this@entry=0x7fffffffe160, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:140
#34 0x00007ffff61cf1c2 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:120
#35 0x0000555555585247 in main (argc=<optimized out>, argv=<optimized out>) at ./kate/main.cpp:644

Created attachment 123782 [details]
valgrind kate

And here is the valgrind log.

The problem is either in uim, or in the uim platform input plugin for Qt.

Can you please test and confirm if this issue is still occurring or if this bug report can be marked as resolved. I'm setting status to "needsinfo" pending your response, please change back to "reported" or "resolved" when you respond, thanks.

Created attachment 133357 [details]
attachment-15042-0.html

The bug still occurs.

libqt5.* liraries are version 5.15.1+dfsg-2
libkf5.* are 5.74.0-2+b1
uim.* are 1.8.8-6.1

--
David

Forgot to change the Status.

Is this still reproducible?

Wayland support has matured a lot and 2 years have passed so maybe this is no longer a crash.

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

This bug has been in NEEDSINFO status with no change for at least
30 days. The bug is now closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

Thank you for helping us make KDE software even better for everyone!