I'm a happy user of WatchOS 4 on my Apple Watch series 1 and, till iOS 12.1, I've never had a problem syncing my not updated Apple Watch with my updated iPhone.
Now I updated my iPhone to iOS 12.2 and, immediately and in background, without any notify, iPhone started updating my Watch to last version (and automatical updates were disabled!), when I saw it I tried to stop it and the only way to stop the update, suggested by iPhone, has been to unpair the Watch from iPhone. Now I'm trying to pair my Watch again but, as soon as I start pairing, iPhone ask me to update the clock and, refusing, the only choice I have is to unpair the Watch.
Has anyone found a way to keep using an old version of WatchOS with iOS 12.2?