In the parks all week including today. Zero issues with the app or web site. Refreshed / updated FP+ all week long, getting FOP, Na'vi, Slinky Dog and tons of other stuff. Did mobile ordering, made ADRs (and canceled others). Upgraded tickets to APs, got messages from Disney about the Wine and Dine races and possible traffic issues and checked room charges regularly. Not a single outage, reload or issue - except for spotty wifi.
Obviously, your mileage will vary, but there's been no problem on property for us.
Steve