It is exactly after 2 Hours, every time and it is not for short time, it drops for ever until I restart SRBminer.
Anyway, if you are sure it is not related to DevFee, then it is something what happens about that timeframe.
Khm, after this i don't know what to think, if you say it's ALWAYS this way.
Can you try to switch to another pool (pressing p) when this happens? Im curious what will happen if you disconnect/connect to a pool again.