Hashrate Randomly Drops While Mining

I’m mining with an R9 270. When I first started Claymore, it ran at around 180-190h/s (what it should be), then it dropped to 70-80h/s randomly (in claymore, not on flypool. Flypool hashrate rises and falls accordingly with the Claymore hashrate, taking into account fluctuation). Restarting, I got 70h/s. Another restart, and 130h/s (I let it run for a couple of hours each time, remained stable). Several restarts and hashrates later, I got back to 180-190, but it dropped down to 100, then 70 after about 18-20 hours of mining. It’s an inconsistent pattern that I can’t figure out. There’s no throttling, same issue without an overclock, GPU usage stays the same, nothing to do with usage.

Any ideas on what could be the cause? I’m at my wits’ end.