Syncing 50+ wireless sensors
Use broadcast.

As each IMU is logging its data, ensure that data includes a timestamp from its internal counter.

Even though all these counters will drift slightly relative to each other, they will be close enough that a missing timestamp in the logged data from any single unit will be easily detectable - unless all 50 units fail to receive a broadcast tick.

This way, while you can't guarantee complete integrity you can effectively guarantee to detect any missed events in the logged data.