[regression in 5.14] WebEngine fails to recover after suspend

After I suspend and resume (on a Linux laptop with NVIDIA proprietary drivers), any application using QtWebEngine Widgets fails to paint anything.

This happened initially with kmail but I can reproduce it with the simplebrowser example.

The debug output says:

WARNING: QQuickWidgetPrivate::render|?libQt5QuickWidgets.so.5?|QQuickWidget::timerEvent QQuickWidget: Cannot render due to failing makeCurrent()
WARNING: QPlatformBackingStore::composeAndFlush|?libQt5XcbQpa.so.5?|QWidgetRepaintManager::flush composeAndFlush: makeCurrent() failed

(and that last line repeats many times).

If I switch to another virtual desktop and come back, both errors happen again.

The only workaround is to restart the app completely.

This used to work with Qt 5.13, I don't think I changed my nvidia driver since. Can't really check though, recompiling webengine is no picnic.

This does not happen with a simple QtQuick example.