The standard questions...
Are all set to compute mode - or else using block chain drivers.
Are all memory overclocked?
For me the easiest way now is to use fairly recent drivers (Adrenalin 18.3.4 atm) and set every thing in the config (all clocks and volts and ensure compute). Config set up all in the readme with the miner.
I am using linux. So drivers should not be the issue. But as I see in SMOS the slow ones are running at a slow memory (200mhz) and I somehow cannot change this.