Hello hurri10209,
I've got the same model of NVR as you and I'm seeing the same problems you're experiencing. I think I've identified part of the problem I'm getting and I'd be interested to know if the same thing works for you.
Having read through this thread, if my understanding is correct, you have 4 cameras which were originally connected to the PoE ports D1, D2, D3 and D4 on your NVR and you were experiencing drop outs and lagging Live View images from all 4 cameras.
You then mention connecting a 5th camera (fisheye) to your NVR and that worked fine without any problems. Did you connect that 5th camera to PoE port D5?
If you did then try connecting your original 4 cameras to PoE ports D5, D6, D7 and D8. Do not use ports D1 to D4 or D9 to D12
Please let us all know what happens because if your system works ok after trying this method then this would be valuable information to help narrow down the cause.
Thank you.
John H.