Where did you see the "go back to previous version" screen? I don't have anything overly critical on my Hubitat Hub yet, so after seeing your post I gave the update a try too and mine seems to be stuck on the loading screen as well. (It's only been 3-5 minutes, so I'll give it a few more before trying anything else)
Bruce. I haven’t power cycled my hub yet… should I go ahead and do that and then navigate to :8081 and select 678 (if it doesn’t come back up after a power cycle)? Wasn’t sure if you guys might want any diagnostics off it before I power cycled.
I selected 670 and hit submit and it said it would redirect me in 20 seconds. I was redirected and back at the loading screen then after waiting for a bit the main Hubitat Elevation screen loaded as expected.
I'm about to go back to :8081 and try switching back to 678 now.
So during the upgrade, probably the extraction part, I did the page refresh which took me back to the download button again so I restarted the ugprade process. I am wondering if that screwed it up.