I can reproduce this on both my desktop (560ti w/ latest 355 nvidia beta drivers), and my laptop (quadro k2100m - 352.30 driver). Both are on Arch w/ testing and kde-unstable enabled. Issue has probably been happening since 5.3/5.2. 

Application: System Settings (systemsettings5), signal: Segmentation fault
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[Current thread is 1 (Thread 0x7ff202454800 (LWP 2587))]

Thread 2 (Thread 0x7ff1ed4fd700 (LWP 2588)):
#0  0x00007ff1fe14418d in poll () from /usr/lib/libc.so.6
#1  0x00007ff1faedf9f2 in ?? () from /usr/lib/libxcb.so.1
#2  0x00007ff1faee156f in xcb_wait_for_event () from /usr/lib/libxcb.so.1
#3  0x00007ff1efa76ca9 in ?? () from /usr/lib/libQt5XcbQpa.so.5
#4  0x00007ff1fe844a9e in ?? () from /usr/lib/libQt5Core.so.5
#5  0x00007ff1fa65e4a4 in start_thread () from /usr/lib/libpthread.so.0
#6  0x00007ff1fe14d12d in clone () from /usr/lib/libc.so.6

Thread 1 (Thread 0x7ff202454800 (LWP 2587)):
[KCrash Handler]
#5  0x00007ff1fd275fff in QQuickItemPrivate::addToDirtyList() () from /usr/lib/libQt5Quick.so.5
#6  0x00007ff1fd2760b3 in QQuickItemPrivate::dirty(QQuickItemPrivate::DirtyType) () from /usr/lib/libQt5Quick.so.5
#7  0x00007ff1fd282ffd in ?? () from /usr/lib/libQt5Quick.so.5
#8  0x00007ff1fea54eb1 in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#9  0x00007ff1fd2800eb in QQuickItem::event(QEvent*) () from /usr/lib/libQt5Quick.so.5
#10 0x00007ff20059500c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#11 0x00007ff20059a4e6 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#12 0x00007ff1fea2589b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#13 0x00007ff1fea27c96 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#14 0x00007ff1fea7be33 in ?? () from /usr/lib/libQt5Core.so.5
#15 0x00007ff1fa1419fd in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#16 0x00007ff1fa141ce0 in ?? () from /usr/lib/libglib-2.0.so.0
#17 0x00007ff1fa141d8c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#18 0x00007ff1fea7c23f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#19 0x00007ff1fea2326a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#20 0x00007ff1fea2b20c in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#21 0x000000000040edeb in main ()


Reproducible: Always

Steps to Reproduce:
1. Open  System Settings
2. Open Display and Monitor
3. Hit Back

Actual Results:  
Hard crashes system settings

Expected Results:  
System settings stays open

This probably started around 5.3.0ish (maybe even 5.2.x) for me. I know there was a QT bug that supposedly fixed this in the latest QT release, but, I it still occurs for me.