vivoactive 5 10.20 - unstable connection and hung

The problem is obvious, and wide spread. They should have roll back the update and let users to go back to older version of the software.

it happends on huawei P30 Pro like every few hours, then on Pixel 8 pro, may be once every week.

I used to own Forerunner 745 and now 965, they have zero problem whatsoever. This is clearly a faulty software upgrade.

beta 11.20 has the same problems for me. no improvement

I dunno if this will help, but being a former sysprog I decided to try to dig in a bit deeper since the disconnections started to happen more and more frequently. I turned on the bluetooth hci log on my Pixel 8 Pro with the intention of trying to capture a log of what was happening when a disconnection happened. I don't have any experience with interpreting bluetooth logs but back in the day I did a fair amount of interpretation of other types of communication protocol logs (e.g. sna, x.25, ethernet, tcp/ip, etc.) so I thought I might be able to spot something, I mean, how much different could bluetooth be.

So anyway shortly after I turned on the log, I had another disconnection and I did capture it in the log. I used wireshark to have a look at it and I did spot a pattern. There's some kind of exchange going on between the phone and the watch where things called attributes are being read. Every time a pairing request pops up out of the blue, the thing that immediately preceeds it is that the phone has asked the watch to write something and the watch responds with INSUFFICIENT AUTHENTICATION and then bam, the next thing that happens is a new pairing request. In case this means anything to anyone (at Garmin, perhaps), here's the relevant section of the log:

7907 387.729571 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) ATT 16 Sent Read By Type Request, Characteristic, Handles: 0x0040..0x0041
7909 387.968090 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) ATT 14 Rcvd Error Response - Attribute Not Found, Handle: 0x0040 (Running Speed and Cadence: RSC Measurement)
7910 387.971297 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) ATT 14 Sent Find Information Request, Handles: 0x0041..0x0041
7912 388.042664 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) ATT 15 Rcvd Find Information Response, Handle: 0x0041 (Running Speed and Cadence: RSC Measurement: Client Characteristic Configuration)
7915 388.073956 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) ATT 14 Sent Write Request, Handle: 0x000d (Generic Attribute: Service Changed: Client Characteristic Configuration)
7917 388.223318 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) ATT 10 Rcvd Write Response, Handle: 0x000d (Generic Attribute: Service Changed: Client Characteristic Configuration)
7918 388.262091 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) ATT 14 Sent Write Request, Handle: 0x0013 (Unknown: Unknown: Client Characteristic Configuration)
7921 388.525763 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) ATT 14 Rcvd Error Response - Insufficient Authentication, Handle: 0x0013 (Unknown: Unknown: Client Characteristic Configuration)
7923 388.530363 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) SMP 16 Sent Pairing Request: AuthReq: Bonding, MITM, SecureConnection, Reserved | Initiator Key(s): LTK, IRK, CSRK, Linkkey | Responder Key(s): LTK, IRK, CSRK, Linkkey
7937 388.574543 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) L2CAP 21 Rcvd Connection Parameter Update Request
7939 388.575608 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) L2CAP 15 Sent Connection Parameter Update Response (Accepted)
7942 388.820397 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) SMP 16 Rcvd Pairing Response: AuthReq: Bonding, MITM, SecureConnection | Initiator Key(s): IRK | Responder Key(s): LTK, IRK
7951 388.843864 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) SMP 74 Sent Pairing Public Key
7954 389.941984 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) SMP 74 Rcvd Pairing Public Key
7960 390.840340 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) SMP 26 Rcvd Pairing Confirm
7961 390.841454 Google_64:f3:3d (Bob's Phone) GarminIntern_82:cf:48 (vívoactive 5) SMP 26 Sent Pairing Random
7963 391.741441 GarminIntern_82:cf:48 (vívoactive 5) Google_64:f3:3d (Bob's Phone) SMP 26 Rcvd Pairing Random

There are several instances of this in the log I captured. I'd be happy to provide a copy of the entire log to anyone who wants to investigate further.

I'm having an email conversation with a Garmin rep. As per instructed, I already sent her an Android debug log with Bluetooth hci logs enabled last month, so they must be aware of what is going on. Last week I asked for a status update on this issue and she told me there was no planned fix yet, but the case is still being investigated. Fingers crossed.

Yes! Same!

Same annoying issue with a Google Pixel 7a, as I read a hardware replacement does not help here? Any luck with the beta software?

I'm on beta 11.11 which recently showed up for me and the problem is still happening. So no, the beta has not helped me so far. I also completely wiped and reinstalled everything on my (Pixel 8 Pro) phone and that didn't help either. 

Any news regarding this? Right now I am only synchronizing my watch once a week or so, because it is too annoying to keep it paired.