Application: kwin_x11 (5.5.5)
 (Compiled from sources)
Qt Version: 5.5.1
Operating System: Linux 4.4.12 x86_64
Distribution (Platform): Gentoo Packages

-- Information about the crash:
Left the computer alone a few hours, when returning there was a dialog telling that kwin crashed

-- Backtrace:
Application: KWin (kwin_x11), signal: Segmentation fault
Using host libthread_db library "/lib64/libthread_db.so.1".
[Current thread is 1 (Thread 0x7f981f5c6840 (LWP 32362))]

Thread 4 (Thread 0x7f980fdbe700 (LWP 32377)):
#0  0x00007f983327548a in QEventDispatcherUNIXPrivate::doSelect(QFlags<QEventLoop::ProcessEventsFlag>, timespec*) () from /usr/lib64/libQt5Core.so.5
#1  0x00007f983327585e in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#2  0x00007f983322a0ba in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#3  0x00007f9833087974 in QThread::exec() () from /usr/lib64/libQt5Core.so.5
#4  0x00007f982dd028b5 in QQmlThreadPrivate::run() () from /usr/lib64/libQt5Qml.so.5
#5  0x00007f983308bea2 in QThreadPrivate::start(void*) () from /usr/lib64/libQt5Core.so.5
#6  0x00007f9834bff434 in start_thread (arg=0x7f980fdbe700) at pthread_create.c:334
#7  0x00007f983494086d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3 (Thread 0x7f980dcbc700 (LWP 32393)):
#0  pthread_cond_wait () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x00007f9832199f34 in QTWTF::TCMalloc_PageHeap::scavengerThread() () from /usr/lib64/libQt5Script.so.5
#2  0x00007f9832199f79 in QTWTF::TCMalloc_PageHeap::runScavengerThread(void*) () from /usr/lib64/libQt5Script.so.5
#3  0x00007f9834bff434 in start_thread (arg=0x7f980dcbc700) at pthread_create.c:334
#4  0x00007f983494086d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 2 (Thread 0x7f980e4cd700 (LWP 899)):
#0  pthread_cond_wait () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x00007f983308c51a in QWaitCondition::wait(QMutex*, unsigned long) () from /usr/lib64/libQt5Core.so.5
#2  0x00007f982e1eb9be in QSGRenderThread::processEventsAndWaitForMore() () from /usr/lib64/libQt5Quick.so.5
#3  0x00007f982e1ec243 in QSGRenderThread::run() () from /usr/lib64/libQt5Quick.so.5
#4  0x00007f983308bea2 in QThreadPrivate::start(void*) () from /usr/lib64/libQt5Core.so.5
#5  0x00007f9834bff434 in start_thread (arg=0x7f980e4cd700) at pthread_create.c:334
#6  0x00007f983494086d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 1 (Thread 0x7f981f5c6840 (LWP 32362)):
[KCrash Handler]
#6  0x00007f983356b460 in QScreen::refreshRate() const () from /usr/lib64/libQt5Gui.so.5
#7  0x00007f982e1e7b88 in QSGThreadedRenderLoop::startOrStopAnimationTimer() () from /usr/lib64/libQt5Quick.so.5
#8  0x00007f982e1e7cb3 in QSGThreadedRenderLoop::animationStarted() () from /usr/lib64/libQt5Quick.so.5
#9  0x00007f983325290a in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib64/libQt5Core.so.5
#10 0x00007f983306998e in QUnifiedTimer::startAnimationDriver() () from /usr/lib64/libQt5Core.so.5
#11 0x00007f983306a759 in QUnifiedTimer::startTimers() () from /usr/lib64/libQt5Core.so.5
#12 0x00007f98332538d1 in QObject::event(QEvent*) () from /usr/lib64/libQt5Core.so.5
#13 0x00007f9833a12a1c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#14 0x00007f9833a17ee6 in QApplication::notify(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#15 0x00007f983322b1ad in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib64/libQt5Core.so.5
#16 0x00007f983322dcf6 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib64/libQt5Core.so.5
#17 0x00007f9833275722 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#18 0x00007f9818eba85d in QUnixEventDispatcherQPA::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5XcbQpa.so.5
#19 0x00007f983322a0ba in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#20 0x00007f983323115c in QCoreApplication::exec() () from /usr/lib64/libQt5Core.so.5
#21 0x00007f9834e19564 in kdemain () from /usr/lib64/libkdeinit5_kwin_x11.so
#22 0x00007f9834877650 in __libc_start_main (main=0x400820 <main>, argc=3, argv=0x7ffd78587258, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffd78587248) at libc-start.c:289
#23 0x0000000000400859 in _start ()

Reported using DrKonqi