From my experience, app rebooking is only dependable when you have a nonstop flight that has been cancelled... Very bad with delays/misconnects/etc...
Also bad when you’re connecting from somewhere and the last leg of your trip gets cancelled.
For example, I was on AA65 DFW-BOS last week which was canceled on the tarmac. I immediately was able to rebook on the first flight the next day... My seat mate was on a GDL-DFW-BOS routing and the app didn’t offer him options despite the fact that he was in DFW and his final destination was BOS.