FYI: This seems to be corrected. What I did was start one at a time removing any feature associated with the CO line that points to the fax detect circuit. The last thing (or combination of?) that seems to have corrected this problem was I changed the CO line ringing assignment to the main admin phone ( CO line associated w/fax detect) to days only (comes default d/n). I had previously determined that the fax detect would work flawlessly until put manually into night mode. After it failed it would not work again until I'd done a system reset. Hope this saves someone else some grief. I could go back and start putting things back to see if it was a combination of things, but I've already spent enough time on this trouble that can't happen (per Vodavi).

Retired phone dude