Hi,
I tried switching to monero from eth mining and it works fine on one of my rig getting 800h/s per gpu but my other rig gets 300ish mhs on all card for 1 second than all but the first card drop 2 0mhs. They're both identical except for GPU brands XFX GTS 580s 8gb vs nitro+ 580 8gb.
Any idea? Ethereum is working fine on both.
Check your virtual memory is set high enough, from what I can remember Claymore's Cryptonote miner needs 8GB virtual memory PER CARD to work , or at least work to its best abilities.
Try your setup with a different miner, this might help fault find where the problem is. I prefer to use SGminer for Monero
https://github.com/genesismining/sgminer-gm/releases .