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?
Which miner do you use for mining?
To use 4 GB sawcards for mining, you need to add these settings to the miners' configuration
TeamRedMiner: --eth_4g_max_alloc=4078
lolMiner: --4g-alloc-size 4078
PhoenixMiner: -daglim 4078
As of today, get a hashrate of 17-18 megahash.
With Ethereum prices above $ 1200, mining on 4GB graphics cards is very profitable.
For another 2-3 weeks, your video cards will generate income when mining Ethereum.