Before that I removed the $HOME/.cache content. Maybe it's somewhat connected.

Thread 1 (Thread 0x7f3e0a2cf8c0 (LWP 3466)):
[KCrash Handler]
#6  0x00007f3e0359a428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#7  0x00007f3e0359c02a in __GI_abort () at abort.c:89
#8  0x00007f3e03d49311 in QMessageLogger::fatal(char const*, ...) const () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#9  0x00007f3e03d443ca in qt_assert_x(char const*, char const*, char const*, int) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#10 0x00007f3d2e65b065 in KActivities::Stats::ResultSetPrivate::initQuery (this=0x2d7fc80) at /home/roman/dev/kde/src/frameworks/kactivities-stats/src/resultset.cpp:140
#11 0x00007f3d2e659e63 in KActivities::Stats::ResultSet::ResultSet (this=0x7ffc1b4002e0, query=...) at /home/roman/dev/kde/src/frameworks/kactivities-stats/src/resultset.cpp:491
#12 0x00007f3d2e8b1c92 in Backend::recentDocumentActions (this=0x1d9f140, launcherUrl=..., parent=0x2d949c0) at /home/roman/dev/kde/src/kde/workspace/plasma-desktop/applets/taskmanager/plugin/backend.cpp:318
#13 0x00007f3d2e8c3d54 in Backend::qt_static_metacall (_o=0x1d9f140, _c=QMetaObject::InvokeMetaMethod, _id=13, _a=0x7ffc1b4005b0) at /home/roman/dev/kde/build/kde/workspace/plasma-desktop/applets/taskmanager/moc_backend.cpp:216
#14 0x00007f3d2e8c4385 in Backend::qt_metacall (this=0x1d9f140, _c=QMetaObject::InvokeMetaMethod, _id=13, _a=0x7ffc1b4005b0) at /home/roman/dev/kde/build/kde/workspace/plasma-desktop/applets/taskmanager/moc_backend.cpp:330
#15 0x00007f3e06fcebf9 in QQmlObjectOrGadget::metacall (this=this@entry=0x7ffc1b400920, type=type@entry=QMetaObject::InvokeMetaMethod, index=index@entry=18, argv=<optimized out>) at qml/qqmlpropertycache.cpp:1732
#16 0x00007f3e06f4b5bd in CallMethod (object=..., index=<optimized out>, returnType=<optimized out>, argCount=<optimized out>, argTypes=<optimized out>, engine=engine@entry=0x17a5030, callArgs=0x7f3dea77b5c8, callType=QMetaObject::InvokeMetaMethod) at jsruntime/qv4qobjectwrapper.cpp:1158
#17 0x00007f3e06f4cc8d in CallPrecise (object=..., data=..., engine=engine@entry=0x17a5030, callArgs=callArgs@entry=0x7f3dea77b5c8, callType=callType@entry=QMetaObject::InvokeMetaMethod) at jsruntime/qv4qobjectwrapper.cpp:1420
#18 0x00007f3e06f4ded0 in QV4::QObjectMethod::callInternal (this=<optimized out>, callData=0x7f3dea77b5c8, scope=...) at jsruntime/qv4qobjectwrapper.cpp:1966
#19 0x00007f3e06f669de in QV4::Object::call (d=0x7f3dea77b5c8, scope=..., this=<optimized out>) at jsruntime/qv4object_p.h:445
#20 QV4::Runtime::method_callProperty (engine=0x17a5030, nameIndex=<optimized out>, callData=0x7f3dea77b5c8) at jsruntime/qv4runtime.cpp:1104
#21 0x00007f3d4c03638e in ?? ()
#22 0x00007f3dea77b500 in ?? ()
#23 0x0000000000000008 in ?? ()
#24 0x00007f3dea77b568 in ?? ()
#25 0x00007f3e06eb8315 in memcpy (__len=<optimized out>, __src=0x7f3dea77b608, __dest=<optimized out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:53
#26 QV4::ExecutionContext::newCallContext (this=0x17a5030, function=<optimized out>, callData=0x7f3dea77b608) at jsruntime/qv4context.cpp:94
#27 0x00007f3e06ebaafc in QV4::ExecutionContext::call (this=<optimized out>, scope=..., callData=<optimized out>, function=0x7ffc1b400c60, f=<optimized out>) at jsruntime/qv4context.cpp:274
#28 0x00007f3e06edcc6e in QV4::ScriptFunction::call (that=<optimized out>, scope=..., callData=<optimized out>) at jsruntime/qv4functionobject.cpp:411
#29 0x00007f3e06f636be in QV4::Object::call (d=0x7f3dea77b500, scope=..., this=<optimized out>) at jsruntime/qv4object_p.h:445
#30 QV4::Runtime::method_callActivationProperty (engine=<optimized out>, nameIndex=<optimized out>, callData=0x7f3dea77b500) at jsruntime/qv4runtime.cpp:1052