I was restarting the ethereum client as I updated to the most recent version. Thus the connection problems.
It was not planned to update and I had to fix it asap, so I didn’t post any news or hints on this.
The previous version was compiled with an older go-compiler, and was producing some kind of buffer overflow when sending reward transactions. No real problem for the workers, but my available server memory was drained due to the overflow.
Things are fixed and work like expected.
Still hoping to pop the next ETH now!