Reproducer attached. Steps to reproduce:
1. Build project "ctrl" so that it is registered as ActiveX server (need administrator privilege so probably better to qmake and nmake from CMD)
2. Add <Qt installation>/<Qt version>/msvc/bin folder to PATH and load mfc.sln (need MFC libs)
3. Build and run MFC application.
4. Drag and try to resize QTableWidget rows/columns. Application stops responding immediately afterward.

Nevertheless, the registered server works perfectly in testcon. One can insert control "TableCtrl" into testcon and see that dragging and resizing works perfectly there. So I suppose the problem is not ActiveQt itself but in the integration of it into MFC (or the MFC itself?).

According to customer, the problem starts from Qt 5.15.9. Older Qt versions (5.15.7, 5.15.8) are unaffected. So it sounds like a regression of Qt. But considering the result from testcon, it also seems like a MFC issue. Need insight from devs.