I went to talk to alex and when I came back kwin crashed. I think it happens when the screen goes idle.

Thread 1 (Thread 0x7f39181bd800 (LWP 1024)):
[KCrash Handler]
#6  0x00007f390d1b3d67 in raise () from /usr/lib/libc.so.6
#7  0x00007f390d1b5118 in abort () from /usr/lib/libc.so.6
#8  0x00007f390e483708 in qt_message_fatal (context=..., message=...) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/global/qlogging.cpp:1364
#9  0x00007f390e481306 in QMessageLogger::fatal (this=0x7fff44b7e9f0, msg=0x7f390e786128 "ASSERT failure in %s: \"%s\", file %s, line %d") at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/global/qlogging.cpp:669
#10 0x00007f390e47ba41 in qt_assert_x (where=0x7f3917d74692 "QVector<T>::operator[]", what=0x7f3917d7457e "index out of range", file=0x7f3917d74550 "/home/kde-devel/kde5/include/QtCore/qvector.h", line=385) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/global/qglobal.cpp:2132
#11 0x00007f3917c2661f in QVector<QMap<KWin::Group*, KWin::Layer> >::operator[] (this=0x7fff44b7ead0, i=1) at /home/kde-devel/kde5/include/QtCore/qvector.h:385
#12 0x00007f3917c243c5 in KWin::Workspace::constrainedStackingOrder (this=0x13e4620) at /home/kde-devel/frameworks/kwin/layers.cpp:514
#13 0x00007f3917c22a7a in KWin::Workspace::updateStackingOrder (this=0x13e4620, propagate_new_clients=false) at /home/kde-devel/frameworks/kwin/layers.cpp:119
#14 0x00007f3917c791ed in KWin::Client::setGeometry (this=0x1436e60, x=0, y=0, w=1280, h=800, force=KWin::Client::NormalGeometrySet) at /home/kde-devel/frameworks/kwin/geometry.cpp:1953
#15 0x00007f3917c06272 in KWin::Client::setGeometry (this=0x1436e60, r=..., force=KWin::Client::NormalGeometrySet) at /home/kde-devel/frameworks/kwin/client.h:1220
#16 0x00007f3917c7a090 in KWin::Client::blockGeometryUpdates (this=0x1436e60, block=false) at /home/kde-devel/frameworks/kwin/geometry.cpp:2096
#17 0x00007f3917c0609e in KWin::GeometryUpdatesBlocker::~GeometryUpdatesBlocker (this=0x7fff44b7eec0, __in_chrg=<optimized out>) at /home/kde-devel/frameworks/kwin/client.h:1030
#18 0x00007f3917c7b8bd in KWin::Client::changeMaximize (this=0x1436e60, vertical=false, horizontal=false, adjust=true) at /home/kde-devel/frameworks/kwin/geometry.cpp:2358
#19 0x00007f3917c73761 in KWin::Client::checkWorkspacePosition (this=0x1436e60, oldGeometry=..., oldDesktop=1) at /home/kde-devel/frameworks/kwin/geometry.cpp:1062
#20 0x00007f3917c6ebdd in KWin::Workspace::updateClientArea (this=0x13e4620, force=false) at /home/kde-devel/frameworks/kwin/geometry.cpp:239
#21 0x00007f3917c6eda7 in KWin::Workspace::updateClientArea (this=0x13e4620) at /home/kde-devel/frameworks/kwin/geometry.cpp:253
#22 0x00007f3917c6e008 in KWin::Workspace::desktopResized (this=0x13e4620) at /home/kde-devel/frameworks/kwin/geometry.cpp:81
#23 0x00007f3917d6a9f0 in KWin::Workspace::qt_static_metacall (_o=0x13e4620, _c=QMetaObject::InvokeMetaMethod, _id=79, _a=0x7fff44b7fb50) at moc_workspace.cpp:479
#24 0x00007f390e6f19c9 in QMetaObject::activate (sender=0x13edf20, signalOffset=3, local_signal_index=1, argv=0x0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:3680
#25 0x00007f390e6f11ea in QMetaObject::activate (sender=0x13edf20, m=0x7f3918035760 <KWin::Screens::staticMetaObject>, local_signal_index=1, argv=0x0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:3546
#26 0x00007f3917d5f515 in KWin::Screens::changed (this=0x13edf20) at moc_screens.cpp:249
#27 0x00007f3917c3f89f in QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, void (KWin::Screens::*)()>::call(void (KWin::Screens::*)(), KWin::Screens*, void**) (f=(void (KWin::Screens::*)(KWin::Screens * const)) 0x7f3917d5f4ec <KWin::Screens::changed()>, o=0x13edf20, arg=0x7fff44b7fea0) at /home/kde-devel/kde5/include/QtCore/qobjectdefs_impl.h:508
#28 0x00007f3917c3f832 in QtPrivate::FunctionPointer<void (KWin::Screens::*)()>::call<QtPrivate::List<>, void>(void (KWin::Screens::*)(), KWin::Screens*, void**) (f=(void (KWin::Screens::*)(KWin::Screens * const)) 0x7f3917d5f4ec <KWin::Screens::changed()>, o=0x13edf20, arg=0x7fff44b7fea0) at /home/kde-devel/kde5/include/QtCore/qobjectdefs_impl.h:527
#29 0x00007f3917c3f79f in QtPrivate::QSlotObject<void (KWin::Screens::*)(), QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) (which=1, this_=0x13ee9d0, r=0x13edf20, a=0x7fff44b7fea0, ret=0x0) at /home/kde-devel/kde5/include/QtCore/qobject_impl.h:151
#30 0x00007f390e6f4649 in QtPrivate::QSlotObjectBase::call (this=0x13ee9d0, r=0x13edf20, a=0x7fff44b7fea0) at ../../include/QtCore/../../../../frameworks/qt5/qtbase/src/corelib/kernel/qobject_impl.h:132
#31 0x00007f390e6f18bc in QMetaObject::activate (sender=0x13edf20, signalOffset=3, local_signal_index=0, argv=0x7fff44b7fea0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:3666
#32 0x00007f390e6f11ea in QMetaObject::activate (sender=0x13edf20, m=0x7f3918035760 <KWin::Screens::staticMetaObject>, local_signal_index=0, argv=0x7fff44b7fea0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:3546
#33 0x00007f3917d5f4e9 in KWin::Screens::countChanged (this=0x13edf20, _t1=2, _t2=1) at moc_screens.cpp:243
#34 0x00007f3917c3f2f9 in KWin::Screens::setCount (this=0x13edf20, count=1) at /home/kde-devel/frameworks/kwin/screens.cpp:117
#35 0x00007f3917c40bb9 in KWin::XRandRScreens::update<KWin::Xcb::RandR::CurrentResources> (this=0x13edf20) at /home/kde-devel/frameworks/kwin/screens_xrandr.cpp:69
#36 0x00007f3917c3fd34 in KWin::XRandRScreens::updateCount (this=0x13edf20) at /home/kde-devel/frameworks/kwin/screens_xrandr.cpp:120
#37 0x00007f3917d5f744 in KWin::XRandRScreens::qt_static_metacall (_o=0x13edf20, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7fff44b800c0) at moc_screens_xrandr.cpp:67
#38 0x00007f390e6f19c9 in QMetaObject::activate (sender=0x13ee770, signalOffset=3, local_signal_index=0, argv=0x0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:3680
#39 0x00007f390e6f11ea in QMetaObject::activate (sender=0x13ee770, m=0x7f390eb921e0 <QTimer::staticMetaObject>, local_signal_index=0, argv=0x0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:3546
#40 0x00007f390e780eed in QTimer::timeout (this=0x13ee770) at .moc/moc_qtimer.cpp:191
#41 0x00007f390e6fc809 in QTimer::timerEvent (this=0x13ee770, e=0x7fff44b80ac0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qtimer.cpp:255
#42 0x00007f390e6eb1b2 in QObject::event (this=0x13ee770, e=0x7fff44b80ac0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qobject.cpp:1222
#43 0x00007f390f519698 in QApplicationPrivate::notify_helper (this=0x130d880, receiver=0x13ee770, e=0x7fff44b80ac0) at /home/kde-devel/frameworks/qt5/qtbase/src/widgets/kernel/qapplication.cpp:3501
#44 0x00007f390f516ec4 in QApplication::notify (this=0x7fff44b80dd0, receiver=0x13ee770, e=0x7fff44b80ac0) at /home/kde-devel/frameworks/qt5/qtbase/src/widgets/kernel/qapplication.cpp:2954
#45 0x00007f3917c295be in KWin::Application::notify (this=0x7fff44b80dd0, o=0x13ee770, e=0x7fff44b80ac0) at /home/kde-devel/frameworks/kwin/main.cpp:344
#46 0x00007f390e6affa6 in QCoreApplication::notifyInternal (this=0x7fff44b80dd0, receiver=0x13ee770, event=0x7fff44b80ac0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qcoreapplication.cpp:935
#47 0x00007f390e6b3bcd in QCoreApplication::sendEvent (receiver=0x13ee770, event=0x7fff44b80ac0) at ../../include/QtCore/../../../../frameworks/qt5/qtbase/src/corelib/kernel/qcoreapplication.h:237
#48 0x00007f390e724a6a in QTimerInfoList::activateTimers (this=0x134c0c8) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qtimerinfo_unix.cpp:643
#49 0x00007f390e7229c5 in QEventDispatcherUNIX::activateTimers (this=0x13401b0) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qeventdispatcher_unix.cpp:557
#50 0x00007f390e722d32 in QEventDispatcherUNIX::processEvents (this=0x13401b0, flags=...) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qeventdispatcher_unix.cpp:619
#51 0x00007f39013124e2 in QUnixEventDispatcherQPA::processEvents (this=0x13401b0, flags=...) at /home/kde-devel/frameworks/qt5/qtbase/src/platformsupport/eventdispatchers/qunixeventdispatcher.cpp:70
#52 0x00007f390e6accb0 in QEventLoop::processEvents (this=0x7fff44b80cf0, flags=...) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qeventloop.cpp:136
#53 0x00007f390e6acf89 in QEventLoop::exec (this=0x7fff44b80cf0, flags=...) at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qeventloop.cpp:212
#54 0x00007f390e6b065e in QCoreApplication::exec () at /home/kde-devel/frameworks/qt5/qtbase/src/corelib/kernel/qcoreapplication.cpp:1188
#55 0x00007f390ec8a32c in QGuiApplication::exec () at /home/kde-devel/frameworks/qt5/qtbase/src/gui/kernel/qguiapplication.cpp:1436
#56 0x00007f390f5166f1 in QApplication::exec () at /home/kde-devel/frameworks/qt5/qtbase/src/widgets/kernel/qapplication.cpp:2746
#57 0x00007f3917c2acd5 in kdemain (argc=1, argv=0x7fff44b813f8) at /home/kde-devel/frameworks/kwin/main.cpp:555
#58 0x0000000000400cf8 in main (argc=3, argv=0x7fff44b813f8) at kwin_dummy.cpp:3

Reproducible: Always