I receive a weird reply from one of the user, that says one of our watch faces (written in HTML) disconnect his watch face and phone. Is it even possible?
Any advice for us is welcome.
From my experience is not possible. Connection with paired phone works over 3rd party apps and watch faces. It is managed by system. Your app have to turn off Bluetooth or event. WIFI connection but it is not possible programmatically because security reasons.
Maybe ask your customer for change watch face to another one and observe what happens then.