When you say you unpaired the Watch, do you mean you actually unpaired it from the iPhone or unpaired it in the Devices & Simulators window in Xcode?
I recently had a bunch of those errors, and the fix for me was to do the following. Note, this took about 12 hours overnight for it to "self-heal," so you may also have to try again in the morning.
Unpair the Watch in Xcode, in the Devices & Simulators window.
Click the + button in the bottom-left of that window. Your Watch will not be listed.
Close the windows and quit Xcode.
Re-launch Xcode.
Re-open the Devices & Simulators window.
If your Watch is not automatically listed as a disconnected device, click the + button again.
If your device is listed and available to set up, click Next to do so. Your Watch should now work normally with Xcode.
If your device is not listed, quit Xcode, wait about 12 hours, and try again.
I don't know why it took so long, but I was sitting there trying to add it again for at least an hour, quitting Xcode and retrying, rebooting the Mac and retrying, to no avail. But the next morning, it just worked.