Heh, I didn't even know about that "feature" (never used Dahuas). It wasn't possible to disable the reboot before?
It's a bit funny since I see mostly two things happening:
cameras rebooting at the wrong time (system time not set / drifting)
a big bunch of cameras rebooting at the exact same time.
I hope their reboot doesn't take many seconds. Perhaps you could stand close to one to pinpoint the exact system time, if it makes some noise or blinks while at it. If we generously assume a reboot results in five seconds of lost footage, with time synced between cameras watching over a 30m wide space, a methodical ninja warrior could sprint through without evidence. Then they would patiently wait a week for the two cameras in the next hallway to reboot.