I compiled the CentralWidgetExample, ran it and played around with the docking system. It often gets stuck as shown in this gif:

1. I undock a widget and drop it above the central widget, making it float.
2. I then repeatedly move it, keeping it floating.
3. At some point the layout system gets stuck. This seems to happen randomly, I haven't been able to see a pattern here. Usually it takes longer than this, but I kept this recording to keep the gif short.
4. The layout system is then stuck on top. I can't click anything below it. It captures all clicks on top of its bounding box, but ignores them.
5. I am able to move the parent window, but only by clicking its titlebar outside of the layout system's bounding box, as can be seen in the gif.
6. Closing the main window also deletes the layout system, so that's ok.

I see the following warning on stdout when compiled with Qt 6.1.3: qt.core.qobject.connect: QObject::connect: No such signal QComboBox::activated(const QString&) (line is Qt-Advanced-Docking-System/examples/centralwidget/mainwindow.cpp:99), but I don't know if that has anything to do with this problem.

It doesn't only happen with CentralWidgetExample: before I tried that one I had the exact same problem with a simple program I built that is similar to the Getting started example

I tried this on Qt 5.12.5 and Qt 6.1.3, and built ads both in debug and release. I'm using the latest commit for ads, b5b251d.
My system is Kubuntu 20.04.2 with kernel 5.4.0-80. My display manager is sddm. If it helps: I'm on dual 1440p screens and it happens with the application both on my left and right screen. I've got a good mouse so I don't think it's a button bouncing issue.