I was away for a while, but posting just to close the topic, if anyone would have similar problems.
The issue was (as expected) that the video output (monitor) was connected to one of the 4GB GPUs.
Since this rig has 8 x 4GB cards, I have connected the monitor to the motherboard and have switched to HiveOS.
This has worked for short time, but then I suppose the DAG file became too big. Due to some time away, I have turned off the rig.

Now that I am back, does anyone know if plugging 8GB card in the 1st slot will keep the 4GB cards mining ETH in the future, I suppose not?