Does anyone have an idea what can lead to this hashrate?

All chips seem to be fine. It is powered by a 1600W PSU (all 4 PCIe Cables connected), but it is only ~half of the promised hashrate.
Latest firmware is also installed...
Kind regards
Have you tried a lower diff? you seem to be discarding most of your work due to a high diff selected at ghash.io.
Ok I looked at all of my units 7 in all and the HW errors and utility are the big differences, yours show huge HW errors compared to mine in 5 days show <300 vs your >4700 in half the time and my utility is 23 verses your 13.
So you should open a case with Bitmain as something is very wrong.
Does your power supply use a single 12v rail ?