Hello,
I am having the same problem, running a widget application on Windows 10 (Qt 5.11.2 or 5.9.4, same problem). A lot of users are complaining too. I can reproduce this, strangely enough I just have to launch another specific application (not developed by us) and it corrupts all menus and widget in our app. Only solution is to restart the application, or to start our application after the other app. It also corrupts QtCreator menus and fonts, but a bit less, I guess because I am using a custom style derived from Fusion Style. This occurs only on Windows 10, not MacOS, nor Linux etc. Unfortunately most of my users are also using this other application. My PC is equipped with a NVIDIA board (GTX 950M) but I doubt it comes from that.

My PC is a laptop with an external screen connected through a HDMI cable. If I disconnect the HDMI cable the display returns of course on the laptop screen. When I reconnect the external screen, again all menus and widget get corrupted in our app and in QtCreator (but somehow a bit "less" than in the previous case).

I have tried hard to find what event is triggered but couldn't find anything useful. Any help or suggestion will be highly appreciated.

Thanks
Philippe.