On my windows PC that i also mine from.. for whatever reason on some windows installs I would hash ethash algo normal for a little while then it would snap and eth / etc hashrate would crash but exp, pirl, musicoin etc the hashrate was normal. So if the same thing is happening to you then mining on claymore it would mine your normal hashrate then crash the hashrate on while mining the dev fee for claymore.. then go back to normal when you connect back to your normal pool. I never figured out what caused this but i no longer have this issue.