The mobile app does not sync, it updates data you enter using it in real time with the on-line member tree program.

Turn off auto-sync between FTMM2 and the ACOM on-line member tree program.

Choose when to sync your data between FTMM2 and ACOM on-line member tree program. There are better times than others. Remember, the servers can get slammed at times, so pick a quiet time to sync and you should be fine.