I was having the classic ios13 issue of it disconnecting from the Connect app any time is was closed or the phone restarted, and having to sign in and connect the device every time, but the watch was still connected to the phone itself and still receiving notifications etc. Then I one day I had trouble getting it to reconnect to the app - I would go through the setup process and it always ends up on a screen telling me that there is no bluetooth connection. It says this instantly, with no searching, despite the fact that bluetooth is definitely on, and at the time the watch was still actually connected to it!
I've since tried restarting both devices, closing the app multiple times, turning bluetooth on and off on both devices, and eventually asking it to 'forget this device' in both the iPhone settings and the Connect app. After doing this the watch paired with the phone again but still not with the app, so I 'forgot this device' again, and now the watch won't even appear in the iPhone bluetooth settings page at all (I've tried initiating pairing from the watch, from the phone, and from the app - nothing).
I've now done a hard reset on the watch but it still won't show up on the phone at all... I thought I might try updating the watch software through Garmin Express but it says it's up to date with version 4.9 (despite the fact that Garmin says version 5 has been out for over a month). The Connect app is up to date and I'm running iOS 13.2.
Any ideas would be welcome! Thanks in advance