I have similar issue with QTBUG-65943, QTBUG-59181 with a complex application with lots of Quick2 controls and mapboxgl map, 
Some time after a lots of tab navigation main thread will stuck on QQuickItemPrivate::nextPrevItemInTabFocusChain, right now i found that setting activeFocusOnTab to false would eliminate the problem but it totally disabled tab navigation and this isn't good.

the problem will occur when i constantly push tab button on keyboard and then click on button which will hide the active dialog,

I can confirm this problem exists in 5.13.0 and 5.14.1

The active window is consist of several check boxes and text inputs and actually its preference dialog of application.