Hello, this has been happening to me for months.
I used my Garmin Forerunner 245 watch to provide heartbeat and SpO2 data to Sleep for Android with no issues on my Motorola g(6) Play (Android 9).
Since I upgraded my phone to a Motorola g (10) (Android 11), the tracking only works for about 15 minutes at the most and then the watch shows a symbol of the Garmin IQ with an exclamation mark, when it probably loses some way of connection and stops the data logging in Sleep for Android.
I’m happy to provide more details if you can tell me how. I can reproduce the error every night (: