Set the cameras to have a static IP as it sounds like you have them setup for DHCP.
The camera might not be getting proper power and therefore randomly shutting down and starting back up.
If your using PoE sometimes putting the injector closer solves the problem as some injectors can't handle 100ft of ethernet I've learned (this also includes crap/cheap ethernet cable).
EDIT: Even PoE injectors that say they can handle 300 ft I've had problems with.