We upgraded from 3.7.5 to 4.2.1 and now see a lot of NOT_READY and INTERNAL_ERROR errors in our Live game. According to Unity Cloud Diagnostics, the errors seem to occur more often on Android than on iOS. Ads do work after application start, but putting the app into background for a few hours and then into foreground again, causes that Ads stop working and to display the NOT_READY and INTERNAL_ERROR errors. When the NOT_READY error occurred, I call Advertisement.Load(id, this), which does not trigger OnUnityAdsFailedToLoad, so I assume loading the video was successful. However, Advertisement.Show(id, this) will end up triggering OnUnityAdsShowFailure with the error code. Restarting the app will then make Ads work again in most cases. What can I do that Ads works always?