Same problem here. The belt is easily paired with the watch but when I start activity, it connects only once for 2-3 sec per couple minutes. Then disconnects… and over and over again.
The battery change was the first thing I did when noticed unstable connection, but it didn’t help at all.
The belt has worked fine with Garmin Fenix 5 and Wahoo Bolt v2 for the last year. I also tested it positively with my wife’s Garmin Forerunner 45s, so definitely the belt is not the issue here.