Does anybody have issues maintaining hashrates on Ethereum?

I just got a new MSI Radeon VII (Samsung memory) and it's unable to hold hashrates, even at stock, no matter what driver or miner I use. This contrasts greatly with my Sapphire card (Hynix memory), which is going at 93MH/s VERY stably. On both cards, I've swapped the cooler for AIO watercooling blocks, which has kept junction temps around 60 degrees C.

On the MSI, I've got the following settings: 1750MHz core, 962mV; memory at 1050Mhz.

It runs at ~90MHs for about 5-10 minutes, before violently dropping down to 47MHs.

I've noticed that when it drops down to 47MHs and I close Claymore, the core clock is stuck at 1750MHz, even though nothing graphically intensive is running.

I've tried cleaning and reinstalling drivers and swapping between PCI-E slots, and the damn MSI just keeps dropping.

Has anybody experienced this, and does this sound like a dud card?