I've seen a few minor problems with iOS 10, but most of these are inconsistent or only appear for some users:
- Selection color in the set list view is pink instead of blue.
- Set list preview on the Share page is solid gray.
- Built-in speakers don't play any sound if Multi-Route Audio is turned on.
These first two issues don't occur on any of my devices, so I haven't been able to fix them yet. The third issue seems to be a bug in iOS, and Apple is working on it.
I haven't seen any larger issues. I've been developing since iOS 3, and this iOS 10 release has been the least disruptive. (iOS 7 was the worst.)