I too have the same issue, downloaded the new updated version of Watch 5 beta and i am stuck at the Apple logo. It took an eternity to download and verify and when i saw the watch installing i left it for about an hour , both phone and watch on charge and next too each other. It was frozen on the Apple Logo but phone told me it had installed successfully.
Since then (that was Monday night) i have tried everything, hard reset, ping the phone, find the phone, hard reset whilst standing on my head and anything else i could think of, but still stuck on apple logo. Tried the unpair, and it unpaired successfully but to no avail.
Left it to totall discharge and still stuck.
So i guess the problem hasn't been fixed and those of us unlucky enough to be plagued by this will have to send the watch off to be repaired.
Really Apple needs to supply a way to fix this like you can on the phone and pad and every other device.
This is really poor. Any ideas anyone i think i have tried every permutation i can think of.