Some hours ago (25th Dec) all of my rigs dropped ETH hashrate to -30/40%.
Regardless of miner software, the 1070 were hashing at 25mhs and now at 17mhs. Same issue with 1080ti.. from 45mhs to less than 20mhs.
I will try updating drivers, but this looks more related to epoch than miner/driver.
It's probably a problem with vram, GPUs with 6gb or 8gb memory can't be affected, I will advice you find another good miner to give a try, you can download phoenix miner to see how it performs, it's either the epoch or the miner you are using presently