My fenix 5 s plus loses connection with Samsung Galaxy s10. Rebooting both gadgets doesn't work. I have to pair watch and phone everytime (2-3 times a week) which is annoying. I tried to reset both devices, reinstall garmin connect. Nothing works.

+1 fenix 6 sapphire and S9 in my case

I had a ticket with Samsung regarding this issue, which for me started just after an samsung update was installed.
They told me to reset my network settings. Which I did, it solved the issue for me. I have now been running without any issues for more than 3 weeks.

Please note you'll loose all network settings for wi-fi and bluetooth.
On Samsung S10 it can be found under:
"Settings" -> "General management" -> "Reset" -> "Reset network settings"

Hope you all get it solved

I tried this but doesn't seem to help. The main issue is that when I try to pair the watch (fenix 3) with my phone, the phone says it is paired abut the watch says "connecting...." and keeps spinning .. it fails to complete the connection a little later

I have the same problem.  New Galaxy Note 10+ and Fenix 5s.  Pairs manually successfully (although multiple retries often required).  However loses connection multiple times per day.  Have to manually reconnect in order to Sync.  Has there been any conclusive solution for this?

UPDATE: I tried resetting the network settings.  It appears to have worked.  1 day later and multiple successful reconnects.  Many thanks to user 5189755.

On Samsung S10 it can be found under:
"Settings" -> "General management" -> "Reset" -> "Reset network settings"

This appears to have worked!!  The phone and watch are now automatically reconnecting (e.g. after a charging period or out of range)

The same problem, it was working fine until phone os upgrade, repairing the phone some times work, but now I can't get it working at all...

Thank you! This was the only thing that worked for me on Samsung S10+

Confirm fixed it for me too, have to reconnect everything though which is a pain

Thanks, I just did the reset and connection is looking much better. Very much appreciated.