Lets see your registration page
The ones on an external switch (assuming Dahua) should use port 37777 as shown (192.168.1.x cams). if connected to the NVR itself, using its own PoE ports, the ports should show corresponding to the channel as shown (10.1.1.x cams)
If things are coming and going, I'd start with the assumptions
1- Possible IP conflicts
2- Possible max'ing out power of switch
3- possible maxing out bandwidth of NVR