when i mine ethereum classic i keep get error with openCL error - cannot allocate big buffer for DAG & not enough gpu memory to place dag.
I use 8g rx580 & rx570 and claymore v15 and windows 10
That's odd for an 8GB card, try to add:
-allcoins etc
or
-allcoins -1
Claymore may be placing both ETH and ETC DAG to each of your Cards.