QtWebEngine rendering freezes under some window managers

Using Qutebrowser (with the QtWebEngine backend) or QupZilla 2.x under EXWM (https://github.com/ch11ng/exwm/), I experience frequent rendering freezes when switching windows.  Resizing the window unfreezes the rendering.

A good way to reproduce is from the duckduckgo start page: It freezes systematically.

General recipe:

• The element under focus must be a text field  and in the screen space, so it must be rendered.

• Switch window with EXWM and switch back to the browser window with the text field: the rendering is now frozen.

• Resizing the window will unfreeze rending.

Some notes:

• Defocusing the text field usually does not trigger the issue.
• Sometimes (not sure what triggers this precisely), after defocusing the text field and focusing on another element, the issue still occurs if the aforementioned text field is in the screen space.
  The issue goes once the I scroll away enough so that the text field does not get rendered anymore.

A similar issue has already been reported and fixed:

https://bugreports.qt.io/browse/QTBUG-57416

As the following Qutebrowser issues suggests the issue still occurs with xmonad and EXWM

https://github.com/qutebrowser/qutebrowser/issues/2131#issuecomment-270284569

https://github.com/qutebrowser/qutebrowser/issues/3158