I have a garmin vivoactive 3 and haven't had a problem with connectivity issues when it was pairs with my samsung note 8. I recently bought the A71 and have found my watch is constantly disconnecting from my phone when it locks. My watch will only remain connected for a few minutes after the phone screen turns off and locks and will then display a message saying it is not connected to the phone.
I have looked everywhere I can through settings. I have ensured that the garmin connect app is optimised and allowed to run in the background. I've looked through optimisation, turned off adaptive battery and made sure the connect app is in the apps that won't be put to sleep and am completely lost as to why my bluetooth turns off. It's becoming very frustrating.