Strange dimmer behavior

We have a SENSOR CEM Dimming Rack with the 48 modules (96 circuits). It must be about 15 years old by now.

Recently I noticed that whenever our ETC ENCORE2 Console was shut down, a lamp on circuit, #80 comes on (full). I can do a CEM Reset to turn it off or it  will go off by itself after about 20 minutes. One msg I saw said #80 "Not Set"!  I replaced the 79/80 dimmer pack to no effect so I'm convinced its a CEM control problem. I even erased all Backup looks just in case somehow something had been set. We actually don't use this function and the clear all did not stop #80 turning on when the DMX signal disappeared. I'm not really sure of what I should/could do next. Ideas most welcome.