It stays connected throughout the day but when I go on runs it disconnects. I have a Samsung Galaxy S23.
I tried all the other advice I could find like stopping the phone from optimising for battery, uninstalling Connect and reinstalling, restarting my watch, I may have reset the watch too.
It definitely seems to be specific to running activities. I don't use Walk much but I tried it once and it stayed connected. It's becoming frustrating as I have a CGM now and a widget to get the data but it can't if the phone doesn't stay connected.
I don't think it had this issue with my old Google Pixel but I didn't have a CGM then so I may not have noticed if it disconnected (plus back then I wasn't running for long and it doesn't happen in the first 10 minutes at least)
It will reconnect after a little bit if I take out my phone and unlock it.
I'm thinking about spending the money on a new one but I shouldn't have to and I'll be so disappointed if the same thing happens with that (if it's somehow my phone which is the issue)