@till: can you give a hint?
The problem is most likely caused by this "... and i deleted many old entries in sys_datalog and sys_remoteaction. ...". The sys_datalog contains all changes of the last 30 days, these changes should not be deleted manually or the system is not able to find the last change and will stop the processing of changes.
You can reset the process queue by changing the value of the field "updated" in the server table to 0.