how are you using that low voltage on the core , yet your power consumption remains very high
I'm ok with my wall power usage closer to 2kw for 12 - rx 5700. But please try to notice dev minning?
Obviously this is a bug in the calculation of the mining speed.
That can be one of the options, but is not enough for me as an answer.
Add this: -lidag 1 -hstats 2 -amd -acm -mode 1 -clKernel 1 -eres 0 -clNew 1 -clf 0 -mi 14 -mt 2 -gt 120
Check your log after two hours when dev mine and write me.
I have 1 x rx 5700 and I can't reproduce your situation. Maybe this bug depends on the count of the GPUs.