That’s indeed the case. Android platform does no longer update when the client size change. Additionally the events OrientationChanged and ClientSizeChanged are no longer fired.
The last version that this worked was 3.5, for some reason MG stripped the entire XNA-compatible functionality of window resizing/orientation handling in order to support user enforced orientation.
For example that’s the code that needs to be there to update the backbuffer.
You can use my nuget build that has all of my changes.