This happens to me quite often, but not on a regular/daily basis.  Out of a week, it may happen on two or three days, and sometimes a few occurrences on that day.  Sometimes just reconnecting works, and other times, I have to actually exit out of the Operator Client and restart the Operator Client.  Also, I find that if I leave my Operator Client connected for a long period of time, I get this issue too.  By "long period of time", I am suggesting in excess of 8 hours.