This sounds like a battery issue. We haven't heard of this happening to anyone else.
Are you calibrating your batteries? Every 20 flights or so you need to run it down to 8% or so to let the battery charge back up fully. If you only ever partially deplete and recharge the battery the aircraft doesn't know everything it needs to about the the current capacity of the cells.
You should open a support case with them that includes your flight recorder logs. You would think that a whole fleet of aircraft falling out of the sky would be reason for concern...
Dave's advice is solid.