Connect 4.37 no longer syncing with with Apple Health.

I also have this same issue: my Garmin Connect app seems to be deleting its data from Apple Health even though it still shows as connected and allowing everything from that app.
I've watched my my Garmin-related data (steps, active energy, resting energy, sleep, heart rate, etc.) disappearing while I had the Apple Health app open on my iPhone. Having uninstalled and reinstalled Garmin Connect, along with Strava and MyFitnessPal several times, I eventually tried having a log at the iPhone logs with the Console app on my MacBook while having the phone plugged in with a USB cable.
There are hundreds of entries relating to the "com.apple.HealthKit" subsystem logged by the ConnectMobile (Garmin Connect) app that all state the following:

"Deleting 1 objects"

These show up after opening the Garmin Connect app... Its not every time though but usually every (anecdotally) 2nd or 3rd time the app is opened... Also, only after what appears to have been a background sync of new data from Garmin Connect into the Health App database.
Having checked the entries related to the Strava app as well, the same behaviour is not presented there. The only process/app that these "Deleting 1 objects" log entries show up for is the Garmin Connect app, so I'm also concluding that the issue is with the Garmin app, rather than the Apple Health app or Healthkit subsystem on the iPhone.

This behaviour has started since the latest update of the Garmin Connect app (4.37.0.28) - I've submitted this to Garmin Support but I don't have any feedback from them about it yet.

Top sleuthing. I doff my cap and thanks for your efforts. Not that I expect Garmin to sort it out properly, even with this wealth of information.

I have some more info to add...

In the Garmin Connect App, navigate to:  

  -> Settings 

    -> scroll all the way to the bottom, under “Tech Details”, 

      -> press “App Diagnostics” 

It outputs a HTML page Titled GCM Diagnostics, with app info and paired device info:

If you press on the triple-verticle-dot icon in top right corner, then press “Share” , you can share/copy the App log and Diagnostics page to another location by Email/Airdrop and so forth…

In the app.log file that I got from my phone, I’ve found the following correlated sets of log entries that appear to show what the app is doing - I’ve highlighted what I think are the relevant operations being performed that are likely to be the cause of the disappearing data

The close proximity of the Delete and Update operations is probably what accounts for the disappearance and reappearance of the data… 

2020-11-18 14:20:15:375 I com.apple.main-thread HealthKitManager:86 Starting HealthKit import

2020-11-18 14:20:15:375 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("DeleteAllSamplesOperation") (operationCount=0)

2020-11-18 14:20:15:375 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHKDataOperation") (operationCount=1)

2020-11-18 14:20:15:375 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateSleepOperation") (operationCount=2)

2020-11-18 14:20:15:375 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHeartRateOperation") (operationCount=3)

2020-11-18 14:20:15:375 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateStepsOperation") (operationCount=4)

--

2020-11-18 18:58:23:995 I com.apple.main-thread HealthKitManager:86 Starting HealthKit import

2020-11-18 18:58:23:995 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("DeleteAllSamplesOperation") (operationCount=0)

2020-11-18 18:58:23:995 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHKDataOperation") (operationCount=1)

2020-11-18 18:58:23:996 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateSleepOperation") (operationCount=2)

2020-11-18 18:58:23:996 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHeartRateOperation") (operationCount=3)

2020-11-18 18:58:23:996 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateStepsOperation") (operationCount=4)

--

2020-11-18 19:27:31:014 I com.apple.main-thread HealthKitManager:86 Starting HealthKit import

2020-11-18 19:27:31:014 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("DeleteAllSamplesOperation") (operationCount=0)

2020-11-18 19:27:31:014 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHKDataOperation") (operationCount=1)

2020-11-18 19:27:31:015 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateSleepOperation") (operationCount=2)

2020-11-18 19:27:31:015 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHeartRateOperation") (operationCount=3)

2020-11-18 19:27:31:015 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateStepsOperation") (operationCount=4)

--

2020-11-19 07:31:58:378 I com.apple.main-thread HealthKitManager:86 Starting HealthKit import

2020-11-19 07:31:58:380 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("DeleteAllSamplesOperation") (operationCount=0)

2020-11-19 07:31:58:381 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHKDataOperation") (operationCount=1)

2020-11-19 07:31:58:381 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateSleepOperation") (operationCount=2)

2020-11-19 07:31:58:382 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHeartRateOperation") (operationCount=3)

2020-11-19 07:31:58:382 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateStepsOperation") (operationCount=4)

--

2020-11-19 08:00:31:413 I com.apple.main-thread HealthKitManager:86 Starting HealthKit import

2020-11-19 08:00:31:415 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("DeleteAllSamplesOperation") (operationCount=0)

2020-11-19 08:00:31:415 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHKDataOperation") (operationCount=1)

2020-11-19 08:00:31:416 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateSleepOperation") (operationCount=2)

2020-11-19 08:00:31:416 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHeartRateOperation") (operationCount=3)

2020-11-19 08:00:31:417 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateStepsOperation") (operationCount=4)

--

2020-11-19 09:18:21:236 I com.apple.main-thread HealthKitManager:86 Starting HealthKit import

2020-11-19 09:18:21:236 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("DeleteAllSamplesOperation") (operationCount=0)

2020-11-19 09:18:21:236 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHKDataOperation") (operationCount=1)

2020-11-19 09:18:21:236 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateSleepOperation") (operationCount=2)

2020-11-19 09:18:21:236 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateHeartRateOperation") (operationCount=3)

2020-11-19 09:18:21:236 V com.apple.main-thread HealthKitManager:152 Will add HealthKit operation: Optional("UpdateStepsOperation") (operationCount=4)

Im having the same issue with syncing to Noom although i have an 8plus

same, my Apple Health only show HR data from Garmin, and it is also missing some dates. All my steps and activities etc all went missing. logged a ticket with support, see what they reply

 I have the same issues on 14.2 AND for testing also on old iOS 9.x with newest garmin version. So definitly something to garmin. 

Please fix that, my Health Insurance gives me a bonus for walking much but they sync with Apple Health App. No other way there. 

Hope you fix that quickly

me too. (Seamless) Apple Health integration was the primary reason I went with Garmin over Fitbit. Please fix this ASAP.

Great news!