Continuing the discussion from Asterisk Audio Problems:
@david551 your (above referenced) post 26 should be marked as the solution as you correctly stated “outside of Asterisk”–as I’m sure you know I cannot mark it as the solution.
My SP kept me running and following-up on tickets from the time the OP expired until now. It has been a harrowing adventure! 
Final status:
After numerous tickets (with my SP) that were closed-out by SP stating “nothing wrong here” and more follow-up (on my part) than I care to document:
And after 4 “tech visits” where the 1st three stated “nothing wrong here” and the 4th arrived during an actual failure event and experienced the issue 1st-hand followed by a lengthy discussion via chat and phone where tech repeatedly experienced push-back from tier-1 engineers and shared my pain.
I finally got through to the correct people and received confirmation from my SP that the problem was on their back-end as had been postulated in the original thread (linked, above), more than once.
The SP finally capitulated and even went so-far as to send me an e-mail to forward to Flowroute stating:
“The issue was related to a back end problem with Gfiber and we had to submit a NOC ticket but that issue has been resolved. This issue was not related to user error or third party devices. I just wanted to apologize for any inconvenience this may have caused you.”
I would mark a solution (in the original thread) but it appears that is not allowed.
My thanks to everyone that helped!
I think that says it all!