Update.
I have been able to cure the problem but I still do not know what was causing it. I went through every Cue in the master playback and modified each by inserting and removing the houselight lanterns. I tried the houselights before and after every modification and the flashing was not present after each modification. My best guess would be that somehow even though the lanterns were not programmed into a cue an effect associated with those lanterns was. It would be nice to know if it was me, my desk or a software problem. I have sent the support team a copy of my modified showfile for comparison. Thank you.