Hmm, that rules out cables as the cause.
Are all your cameras plugged directly into the NVR?
POE powered by the NVR?
The latest firmware for your NVR is here:
DOWNLOAD PORTAL
The EN for English version is the one you need.
I doubt that this is firmware related, but best to bring it all up to the latest version before trying to diagnose any issues.
What firmware version are your cameras running please?