Installed in July 2017 work fine, in September every ten days 1 camera at a time loss video, until all four cameras had no video in October. I have tried all reboot, reset, delete and add cameras, even total disconnect of all cameras and nvr, still no video.
Is this on an outdoor system? Only I had this problem on my 1080 PoE system affecting several cameras. I found moisture had got in the RJ45 connector at the camera end even though it had been waterproofed. I tried cleaning out the socket, but the fault always returned so I eventually cut out the connector and wired the cable directly to the camera. They now seem OK.