Tested with google_maps_flutter 0.5.21-0.5.21+11 on Emulator and Pixel 3a, Android 10.

Steps to reproduce:

• Open app with GoogleMap -> displays ok
• Put app into background, without it being killed by the system.
• Resume the app after a while

Behaviour:

• The map content (base map and custom polygon overlay) is visible for a brief moment, then disappears.
• The Google logo stays visible.
• The map appears to still be there, but be drawn completely translucently. Widgets behind it become visible. Gesture/movement/tap listeners still react to inputs.
• The map can be made reappear by 'wildly' applying zoom-in gestures.
• No specific log outputs.

Note that this is an intermittent problem. I couldn't find a pattern yet as to how long the app needs to be in the background or how much load the device needs to be under (I think it is more likely to happen if the app stays in the background for a longer time, however I had it happen when leaving the app for only a couple of seconds).