I noticed this when trying konversation kf5 on wayland, as it hangs on startup. Konversation uses KIdleTime, and KIdleTime has WidgetBasedPoller which, apart of just not working on wayland (even if it didn't hang), it sets the Qt::X11BypassWindowManagerHint flag, which on qt5 is the same as Qt::BypassWindowManagerHint. The qtwayland QPA plugin doesn't create a wl_shel_surfacel/xdg_surface if a window has that flag, meaning basically that if it draws it will hang waiting for an event from the compositor that will never come, unless you also do some explicit wayland stuff. I'm not sure how you would implement a working KIdleTime backend for wayland right now, but imho it should at least not hang. Happens with Qt(Wayland) 5.4 and 5.5, KIdleTime 5.9.0. Reproducible: Always
This is fixed in multiple ways: 1) Qt doesn't freeze anymore when creating Qt::BypassWindowManager hints 2) There is a KIdleTime implementation for Wayland in kwayland-integration which won't freeze even if the required interfaces are not present.