H/s decreased suddenly

Hey,

All night I had average 279.383 h/s with my amd radeon r9 280x, but 2 hours ago decided to try how another pool ( https://zec.nanopool.org/ instead of https://zec.suprnova.cc), restarted Claymore and speed dropped to 211 H/s.

So I restarted Claymore again , now with original Supernova bat file.. but speed is still low - 211 h/s.

I didn't change any settings, what could cause such drop?

strange, now it is 300 again. Didn't change anything.

Does any of you faced this drop too?