Has anyone ever had a Red AXS rear mech stop pairing and only display the yellow flashing light when you hold the AXS button?
I tried updating firmware and it claims it does it, reads the latest firmware number but still asks for an update in the app. The mech has the warning icon in app.
Kinda seems its stuck in a firmware upgrade cycle or something?
Not exact issue, but I did have an issue with my Red AXS RD that is somewhat similar. When left to go to sleep, it would refuse to wake up. If I reinstalled the battery, it would start working again but only until it went to sleep, then stop again. Updating firmware would complete but then after restarting it would say new firmware available, this sounds identical to your issue.
What helped in my case, though I’ve no clue how/why, was pulling the battery for an extended amount of time. In my case, it took a few days, but then the RD was fine again and I had no more issues with it. The way I found that out was by buying a new RD and leaving the old one sitting around without a battery for a while 
I did read somewhere about shorting the contacts with the battery out, but that did nothing for me. Worth a try…
Amazing, will leave it off the bike for a few days and run the spare (lucky i had one from another build) that i have. I really hope it fixes or its an expensive aper weight 
I did the above, left the battery off for a few days maybe a week until it completely died then it came back to life weirdly.