I get from time to time the message from cgminer, that the stratum pool could not be reached (last time today 21:20 server time)... cgminer is then still continuing mining, but all shares get rejected. When I restart cgminer then, everything is fine and it starts normally mining again.

Is this a problem from the server-side or should I configure cgminer in another way (e.g. that it tries to reconnect more often, ...)?