Hi,
I just read your posted issue in github. First of all I just want to say that the emulator never should be trusted. Always test with a real device. (I don’t know if you’ve already done that already).
Once said that, I’ve tested your code in a tablet and the problem differs slightly to what you mentioned, but still is a problem.
However moving to LaunchMode.SingleTop instead of LaunchMode.SingleInstance seems to fix the problem, at least in my device. (actually it’s the mode I use in the games I’ve released, and never had a similar report)
I hope it helps.
p.s. I had to use AdMob 42.1021.1 because I couldn’t install the latest (I don’t have the latest SDK)