My Edge 510 stopped syncing 4 weeks ago and I’ve tried everything suggested incl deleting an reinstalling the app. What can I do? Super frustrated

Are you getting error messages when it tries to sync?

Try syncing with Garmin Express.

After that try unpairing/pairing using these directions.

Garmin express won’t downlaod on a mobile. Next suggestion please

If you can use a computer and sync with Garmin Express, this is one way to get things updated and hopefully fixed. Also, did you try the steps in the video.? Are you getting error messages when you sync? Can you post a screenshot of the errors?

I. Any even get an error message these days. At times it shows the edge is connected bu it won’t sync and the sync circle won’t highlight

I’ve tried everything you’ve suggested but the 510 still won’t sync. My Garmin vivoactive watch syncs ok. I’ve even deleted it and reinstalled in case that was the problem but it apparently isn’t.

next suggestion please as I’m missing over a months of bike data

I’ve tried everything you’ve suggested but the 510 still won’t sync

Try this. It's on the android forum but most of the steps also apply to iOS: Sync / Connection Troubleshooting Guide

If still not joy, contact Garmin Support directly. They will have you run through some diagnostic tests and probably walk you through a complete factory reset - https://support.garmin.com/en-US/

Before a factory reset, I would consider finding a Windows computer and copy the data from your 510 in the \Garmin\Activity folder to a safe location, since a reset will delete all data and put it back to day one condition.