I'm really confused now, it just happened on VER15 within 15 minutes... With a different USB drive...
To my knowledge this should not be happening since these are 8GB cards and it will hit 3GB DAG file next year for ETH...
I've had these errors once too, but it was OC. Your temps are nice so that's not the issue. Lower both OC and MC with 100, see if it is stable then. If so, go up with 50, MC first.