D800 ip clash?

user_900601872998643

Hi everyone, i have a new RLN8 410 system installed at home with 4 cameras connected to the NVR. The 2 cameras at the front of my property work without fault yet the 2 at the back are trying to share 1 signal line.
i have updated the firmware, deleted all cameras and re-added, tried reboots, restores and hard resets, different cabling and swapping ethernet ports.
The POE tab shows that 4 ethernet ports are all consuming similar wattage but the system only ever displays 3 viewing windows. it seems that the 3rd viewing pane will shuffle back and forth between the 2 rear cameras. All i can find so far from online searches is a possible ip clash, but im struggling to troubleshoot this.
I have made contact with Reolink on this matter but the help process is very slow and i can see it taking a long time.

Any suggestions much appreciated. Thanks.