I have had the same issue. I completely set my schedule a couple of weeks ago on the app (with alternate sessions for many time slots), and when I logged on this week with the rest of my team (who hadn't yet downloaded the app and added their schedule) I noticed that most of my schedule had been wiped.
I still had a few events on my schedule, dinners were there, one session remained on Wednesday, two sessions on Thursday, but 75% of it had been cleared. I chalked it up to either them updating the app or updating the location of the sessions (which you wouldn't think would have cleared it from my schedule).
When I logged on today though the lunches and dinners and keynotes from Wednesday and Thursday were gone, and several of the breakout sessions have also been wiped from both Wed and Thurs.
I have saved my schedule on Outlook as well, and that is what I would encourage people to do in lieu of solely using the app, as there have certainly been issues. Our CSM is looking into it, but it's too close at this point if you have key sessions that you want to attend.
Thanks for letting me know that it wasn't just me, as I hadn't heard of anyone else having problems and was beginning to wonder.