A few years ago I bought my wife a 38mm Apple Watch Series 1. It worked fine until about October. Right around the time we upgraded to WatchOS 5, it accidentally started to lose connection to the phone. It worked well in the last 10 months on the iPhone X. Besides, nothing else seems to have trouble connecting to Bluetooth on the phone.
If we restart the phone or clock, it will usually reconnect. It doesn't seem to be any particular time that it stays connected. Last time it remained connected for about 4 days, it was earlier about 3 hours.
I did the nuclear option and I reset the phone and looked at the factory settings and set them both up new (we did not recover from backup). This solved it for about an hour and a half, and it started to happen again.
Any ideas? The series 0 has never had any problems, but S1 only lasts a few years.
Phone: iPhone X 256GB (Last iOS) View: Apple Watch Series 1 38mm (Last watchOS)