Platform, device version and operating system:
Kindle Fire, Fire HD 8 (8th generation), Fire OS 18.104.22.168
Google Play Store was sideloaded onto the Kindle and Gems of War was installed from there.
Google Account Manager 7.1.2
Google Services Framework 7.1.2
Google Play Services 20.15.16 (040300-309763488)
Google Play Store 20.1.17-all  [PR] 310643216
Screenshot or image:
None. I’ll pursue this if it will help.
What you were expecting to happen, and what actually happened:
I expected the video ad to play in landscape and same way up as the game.
Instead, the video ad played in landscape but upside down relative to the game and the device.
How often does this happen? When did it begin happening?
I can replicate it reliably having narrowed down when it happens (see workarounds below). I think it happens since video ads were introduced, but maybe only since 4.9.5.
Steps to make it happen again
[sorry, this was wrong when originally posted, rewritten]
Turn on auto-rotate display in device settings.
Rotate device to portrait with buttons at top.
Turn off auto-rotate display in device settings.
Start Gems of War.
Rotate device so that buttons are on the right.
Watch video ad.
One workaround is to rotate the device 180 degrees so that buttons are on the left.
Another workaround is to turn on auto-rotate display in device settings.
It is possible that this only happens on Kindle Fire, but I suspect it may happen on other Android devices too.
I note that Gems of War does auto-rotate (landscape only) even with auto-rotate turned off in device settings. Perhaps the video overlay respects this setting but the game does not.