It is normal that on ocasion these messages show up in the execution log, however the OO operation is not impacted by them. The execution log holds events both from the flow executions and the worker events. In the case of worker events the messages may be related to regular self-maintenace of the workers (as in this case) or recovery of the workers.
In case these messages persist you could try increasing the inbuffer capacity and heap size in the wrapper.conf file of the OO component where this is happening (central or RAS). After modifying these values restart the OO service.
As i said increase both heap and inbuffer.
The inbuffer parameter from the wrapper.conf file should look something like this:
Increasing that value should fix things. For more information see the tunning guide.