After updating my Apple Watch to 10.6 my messages are not syncing with my iPhone anymore

I had similar problems. In my case, after updating to 10.6, the watch would not respond to tapping on the face. I rebooted the watch a few times and nothing happened. I was not even able to turn off the alarm. Because it was so annoying, I turned off the haptic alerts. Needless to say, the watch kept showing the alarm. Then, eventually, the watch battery drained out completely shutting off the watch. When I recharged it in a normal way, the problem had disappeared. It looks as if the normal rebooting was not enough because there was still power left to keep whatever caused the malfunctions. I suggest that you drain the watch completely and see what happens. Good luck.