White screen when showing ads on iOS

I get a white screen (no ui - no video) on some reward videos on iOS.
The video starts, but after a few seconds i get the white screen while the audio continues to play. So i guess the video is still playing. There are no buttons, and it never recovers. I don't think it ever happens on the first video, but it happens on the 2nd or the 3rd.

Data:
iOS: 9.3.5
Device: iPad 3
Unity Ads version: 2.1.1
Location: Copenhagen, Denmark
Example ad: Family Farm

Any ideas?