Perhaps your experience with ReSound’s and your audiologist’s feedback has been better than mine. On ReSound Quattros, I had quite a few microphone failures, but with the Nexia, other than accidentally damaging my left HA body microphones, I’ve never had a problem. But with the Quattros, I’d ask for a failure analysis on what went wrong - ReSound would always just warranty replace a failed HA and never say blip.
So, if you got some actual, real feedback on your previous returns, that’s far better than my experience. But maybe they’re just doing the same with you and not digging very deeply into what went wrong.
My disclaimer that I know nothing about how HAs work with CI is that although I might imagine your M&RIE experience is the inverse of mine, I’m clueless about how an M&RIE receiver works with the regular programs and the Hear-in-Noise program with a CI. Do you wear M&RIE receivers in both ears, and the HAs just feed the HA output to your better ear? Since, AFAIK, the Omnia equivalent of the Hear-in-Noise program requires HAs on both ears to work for beam forming. So your setup is a CROS or BiCROS situation besides the CI? (my complete ignorance is showing here).
If the problem were that the M&RIE openings on the receivers were just clogged as GrayGhost suggested, it might be very easy to fix that by just changing out the filters. The circular dot below the receiver wire in the linked picture of my M&RIE receiver is the M&RIE microphone filter.
I replace my M&RIE mic filters ~every 6 months, although I see no ear or hair debris in that region in my daily HA cleaning. I do apply a VERY light coating of olive oil to my molds to ease their insertion into my ear canals, but I wipe my fingers on a Kleenex before inserting the molds to avoid getting olive oil anywhere near the M&RIE mic openings (the sort of possible contamination problem that GrayGhost suggested).
If you only hear sound through the receiver in your better ear, I guess it’s always possible that something about the circuitry in that HA is failing rather than having a M&RIE mic problem.**** If you wear two HAs and you have the problem again where you only can hear using the Hear-in-Noise program, you might try to see if the sound that you can hear is only coming from receivers on one ear or both ears. In my inverse situation in the Hear-in-Noise equivalent, I could only hear sound coming from my right ear, and I could hear nothing coming from my left ear. That made me realize I’d destroyed my left ear body microphones in my half-asleep cleaning of my HAs a few weeks earlier (I stuck my Jodi-Vac needle into the left ear body microphones and on the 2nd one “came to” and said to myself, “What the H---- am I doing?!” But I thought I hadn’t damaged the mics, not realizing that the body mics normally only come into play for me in the Hear-in-Noise equivalent program.).
**** Note: theoretically, the way your audiologist would check receiver function vs. HA body function is by swapping your receiver(s) onto Nexia HAs that she knows work properly and verifying that sound is transmitted to the receiver ~normally in the regular programs like the All-Around (or whatever it’s called with the Nexia). Conversely, she could put a receiver(s) she knows is/are good on your HA body(ies) and see that no programs other than Hear-in-Noise work even with your receiver replaced with a known good receiver. Still, from what little I know, it seems likely that the circuitry in the HA body that takes sound input from the M&RIE microphone and sends it to be processed and sent to the receivers has become defective, as the difference between Hear-in-Noise and the other standard programs is whether the M&RIE microphones are employed (other standard programs) or the body microphones are (Hear-in-Noise program). It’s hard to avoid that distinction when thinking about what went wrong, whehter the problem was in your HA body or receiver.