I've run into trouble with my hashrates:

6 GPU mining rig (4x570, 1x470, 1x480 - all with modded bios'es) on MSI Z270 A Pro, 4GB Ram, Windows 10, AMD 17.6.1 Driver.
PC was working for days now (all on -100 mV, 1150MHz, 2000 Mhz, set with MSI AB). Constantly reporting hashrate of 168 MHs / ~2900 SIA (Dual Mining).
PC was shut down, started again, all settings of AB applied and suddenly a 570 and the 480 making troubles. The hashrate of 2 cards in claymore is changing from 28MHs down to 7ish. RX480 made the system crash, even on stock settings when running claymore for some mins.

I've tryed uninstalling driver, reinstalling (the one what was working before), applying the AMD driver fix, changing back to 4g decoding so all cards reported working again. but the hashrates of these two cards are abysmal.

Now the system is running with 5 gpus (without 480) but the hashrate of one RX570 is fluctuating heavily (see attached screenshot).

Can anybody help?