Ads in PvZ Heroes not working properly

I have this problem with the ads. I can never get all gems available from them because they don't work the way they should. It's almost like every third ad doesn't work. This is the problem:

After watching the ad the game just loads indefinitely and I don't get my 5 gems. I press the X button but then the play ad button disappears and I have to restart the game for it to reappear. Sometimes, this also happens:

When I tap the watch ad button there is a very brief loading but the ad doesn't play, instead the game just returns me to the main screen and again I don't get the gems, however this time the watch ad button is still available afterwards.

I tried resetting the advertising ID and I even reinstalled the game multiple times, it didn't solve the problem.

Is there anything I can do to solve this problem? If not, I hope developers can fix it.

By the way, I am playing the game on Samsung Galaxy J3, Android version 8.0.0.