I am noticing the same problem and spent hours trying to overcome it, before coming here.
One thing that I have noticed, is that on my watch when I go to settings, and choose "Bluetooth", the watch is going in an infinite search loop trying to find Health Devices and regular Devices.
Shame.... because I just paid for the subscription for fitness plus and looking forward to doing some activity! I couldn't even get the videos to play at one point. Yikes!
I was able to get it to work momentarily, but the videos in the fitness plus wouldn't work. Now, nothing seems to work. I am hoping for a fix from Apple.