I've had this with about 5 customers now ...... in all instances, this is the setup
1) Cameras connected to Network Switch
2) Password is not default
3) Firmware is prior to 5.5.0
4) 2 & 4 Line Cameras affected (that I'm aware of)
5) Other cameras attached to NVR directly not affected
6) NVR not affected.
The cameras are going into an 'unactivated' state ...... I first started noticing this around 23rd September ..... interestingly firmware 5.5.0 was released at the same time ..... coincidence? There's no changelog that I could see for that either.