Nope, that wasn’t it.
Checked it in my main project. Set all canvases to SelfHitTestInvisible by hand after changing visibility.
Bug still remains.
Btw this would have meant a major design change, because in 4.8 the canvas obviously didn’t change visibility with it’s parent widget, because everything works like a charm.
Ok, I’ll stick to 4.8 until someone fixes it.
Thanks for your help anyway and have a nice day.