We just got back and had several app issues during our trip. I use the app for pretty much everything (entering the parks, grabbing MaxPass, mobile order, scanning in to rides with FP) so it's pretty noticeable when it's not working. We had several frustrating experiences when trying to get FPs through MaxPass where it would suddenly randomly decide I had no tickets linked, or would randomly have only some of the tickets linked, or that we hadn't bought MaxPass. It would usually resolve itself in 3-4 minutes, and it wasn't that big of a deal since FPs weren't going quickly at all, but it was annoying.
There was also a minor annoyance where mobile orders wouldn't "complete" and they'd still be visible from the main app screen hours later. I'm not sure if that's usual or not.