I have 6 x rx 470 gb custom vbios rig, gigabyte h110 mobo, win10, msi afterburner...etc
Last card in the rig just won’t go over 2.9kH/s whatever I try.
Tried with 4 cards, 5 cards, always the same. Last card in that rig drops down with hash.
No more ideas   
I tried TRM, same issue...
Here is what is happening:
I clean install (DDU) new driver (20.4.2 or whatever), then I patch with new patcher, start miner as admin to switch on compute mode, and while it’s running like that without compute mode all 6 cards work normally but with less hash rate, which is expectable.
AS SOON as I turn compute mode on (with and without restarting the rig), that last card in rig goes down to 2.9kH/s with the rest cards working full 31.5 MH/s.
Whenever I clean DDU reinstall driver and turn compute mode on, that last card drops down with hash.
So every time I turn compute mode on, the last card just won’t go over 2.9kH/s avg.
I tried with and without msi afterburner, all kind of commands (clkernel, clf, altinit...)

At the same time, the other rig with the exactly same 6x rx 470 gb cards, same custom vbios, different mobo/cpu, is working great with 18.12.1.1 driver.
Did anyone have this problem with last card not working and solved it? Can it be that Gigabyte mobo is the problem?
Please help, anyone, throw in few fresh or not so fresh ideas, I didn’t have proper sleep last three days ...
Thank you