Phantom 4 Advanced/Pro, many crashes lately, anybody else?

Hi,

We use our Advanced/Pro drones daily, up to three flights per day, five days a week, we fly 10-15 minute missions primarily for mapping and are careful.

In the past year, three or four of our drones have simply dropped out of the sky for no reason we can think of, the drones simply stop spinning, the screen goes black and they fall, all have crashed beyond repair, one was under warranty, but the upshot is that there appears to be some sort of failure with the drones that is not operator error, and we wonder if other pilots who may fly as often as we do, have had the same thing happen.

This has gotten expensive and is troubling, as you may imagine, DJI could not be bothered to help with an explanation.