Starting dropping my ANT+ power meter last week.

Thank you.  Did not see new Beta is out.  Updated just now.
I will have to check the software version on the road bike P2M.  It was up to date when I checked about two weeks ago. but will double check.
Length of dropout is not long.  3-6 seconds.  
Also the dropouts are few and far between.  But once it happens you then start to doubt the ride info and constantly watch the screen instead of enjoying the ride.  Funny how that works, hahahhaha

if i remember good the #537 is the latest public firmware for NG/NGEco. (there are new betas after it, but that is for internal testing for developers/testers). but soon there will be new stable public version for sure (with new and better app). Do you have any other sensors paired besides the P2M and HR? i mean, DI2, Varia, Remote, etc. Yeah , i know that feeling !!!   if you can share a FIT file (in ZIP format) with me , i will take a look , how does it look exactly. 

I'll share a fit file, no issue. 
And yes.  Loads of sensors.
Basically full set.  Varia, Di2, HR and het P2M

Reading through all of this, I still have not found a resolution for the problem. In my case it's a Bontrager DuoTrap S speed/cadence sensor that continuously connects and disconnects from my edge 840 every 5-10 seconds or so. 840 now running 20.19 version, issue is still there. I have 2 items connected to the 840 when cycling: 1. Garmin HRM heartrate band, no issues at all, and 2. Bontrager DuoTrap S speed/cadence sensor. It worked fine for a few months and now it is constantly connecting and disconnecting. I have it paired through ANT+. I tried deleting and reconnecting, but nothing seems to work, any ideas ? It's extremely annoying,

my issue is solved with the 21.09 beta, the signal ratio (and there are no sensor dropouts even during 4-5hs long rides neither) is increased back to 97-98% where it was with the 9.29 FW (and ruined with the 18.xx upgrade)

but my fear is that others have new issues again with this 21.09 beta, and the next beta or the stable will use the same ant config as the 18.xx-20.xx and the signal ratio will drop again (and the disconnections, drops will appear again...)

Ok, thanks, i may give the beta a try, but does not seems like a solid and permanent solution

did you try this? I just switched to the beta but I still can't connect my powermeter - Assioma Duo - via Ant+. IT just happened all of a sudden this morning - had it, then I didn't (also lost my HR) and I could only get them back via BLT. Problem is Asiomas via BLT don't have all the data that the ANT+ way does it appears. And I tried it on my 830 and it works as it should. I also have a brand new Stages crank which can't work properly, but I think that's a stages problem vs Garmin

21.09 was much better for me. Unfortunately, 21.11 made it worse again. ANT connections to my Rotor power meter were almost non-existent yesterday. Resorted to BLE, and while better, it was still disconnecting frequently. 

that's so garbage. i have zero ANT+ connection but at least (so far) BLT isn't dropping power. I emailed garmin support - i'm sure they know about this but still. we'll see what they say