I have Xiaomi Mi A1 and got an android pie update last week. Since then the bluetooth connection is not working with my Garmin Vivoactive smartwatch. I can initially pair bluetooth with phone using 6 digit number that appears on the watch. But after that nothing happens, the watch does not show bluetooth icon anymore and after some time says 'phone disconnected'. Tried all possible suggested solutions online such as rebooting, resetting, cleaning up caches of apps/bluetooth app, uninstall and reinstall garmin connect app, forgetting and pairing bluetooth again... nothing worked. Not sure if this is an android issue or garmin connect issue. Please let me know if anyone facing similar issue or has found a workaround.
[UPDATE 21 jan 2019] WHAT WORKED FOR ME: I got it working after doing a factory reset of my vivoactive watch!