Multiple OpenGL windows (example: combo box popups in Qt Quick Controls) and using non-toplevel QGLWidgets (example: using it as a viewport for QGraphicsView) is not supported on Android currently, and will cause crashes if you try it.
This is an inherent limitation in the eglfs plugin.
The following attempt at fixing it was tried and abandoned:
Another possible fix would be to use different SurfaceViews for the top levels and let Android handle the composition. This would most likely fix several other issues as well if it can be done.