I've had the App show incorrect boarding times during a misconnect and subsequent reschedule. My flight to SLC was delayed by 90 minutes, so I missed my onward connection. It was the last flight of the day, so I was rescheduled on the first flight the next day. However, the App showed the boarding time for the original flight (~8 pm) and the departure time for the new flight (~6 am). So had I actually followed directions and showed up at the boarding time, I would have been 14 hours late :/

I took a screenshot and sent it to Delta tech support, so hopefully they fixed it - that was over a year ago.