You're not pausing the ads on the AdViews. And with 3 AdViews running it wouldn't surprise me if they confusing each other wrt state. After all Admob policy is only a single AdView. Perhaps that is partly due to technical issues with multiple AdViews making requests in the background at the same time.
You can verify this is the issue by commenting out 2 of the AdViews.
If that's it then, you could try pausing the AdViews.
Or rethink your use case.
William