Hashrate drops consistently until zcashd restart

Hello everyone,

Maybe a stupid question from a stupid old man but… with the v1.0.0-rc2 und the tromp solver, I begin strong at ~10 Sol/s, and my rate then consistently drops over an hour or so… until I restart zcashd, where the whole thing begins again.

I thought this might be due to the testnet difficulty also rising in the background, but I am not so sure…

Any advice is welcome