This has happened to me twice with firmware 1.0.2. This last time it was 10 hours into a Bun Burner Gold. I had the 50S plugged into a Sena Powerbank.
After our next stop I could receive and transmit on mesh and my phone. About 9 hours later I got intermittent sound from the bike.
The low battery warning comes on at about 5 hours but does not cut out as fast as the old 30K did.