Yes, we’ve seen similar problems.
Last January, we were running version 5.4. We found that if we scheduled threads to read only on certain days of the week, they would not run at all in January. We were able to work around this problem by updating the schedule with the days of the month in January that they should run and leaving an asterisk in day of the week. In February, we were able to switch back to the normal schedules.
We are now running 5.4.1 rev1, and we had been told that this scheduling bug wasn’t going to be fixed until 5.6. So, at the end of December we updated our threads to run only on specific days of the month. We tried restarting on December 31 with this schedule, and found that the processes would go into a CPU consuming loop and not process any messages. So, we switched to our normal schedules and everything ran OK.
On January 1, we saw that the threads still seemed to be running OK with the normal schedule, so we left this schedule in place. However, I think that we did some additional things to try to clear up our problems like reinitializing the site.