I have two AW Series 2 (one SS one Alum) and an iPhone X. The are both having the same issue - they will disconnect from the iPhone X for no reason. I can usually get them to reconnect by turning on and off Airplane Mode, but it is annoying. I have spoken to Apple Support - they had me erase all three devices and set them up as new. It seemed to work better for a while, but as soon as I reconnected the second Apple Watch (the SS one), it started up again. A second call to tech support agreed that the issue was probably the iPhone X - as it was happening to both AW - and I had an appointment at the Genius Bar, they ran some diagnostics on the iPhone and gave me a replacement. Well, it's happening again with the replacement iPhone X. Not as often, but still with both watches. Any suggestions?