iOS10 does not display certain types of PDF files correctly. (This is fixed with 10.2)
There seems to be an issue with color PDFs. Apparently iOS10 is grabbing way more memory than before. This is a problem and right now, the only answer seems to be to make sure you have grayscale documents. Will report to Apple and hopefully they will fix this. This causes slower page turns and crashes after a while. (10.2 seems to address this - will have more confirmation shortly). The public beta of 10.2 is available: https://beta.apple.com/sp/betaprogram/guide#ios
Recordiing mp4 distorts with iPad Pro. Checking on this. (Fixed with 10.2)
The metronome had a problem with iOS10 and was fixed with unrealBook 2.6.