Did the back up first on the C7, both to the cloud and to a local file.
On the C8, I first tried to restore from a local file. Seemed to work, but I could never get past pages demanding that I register (I registered on the C7 long time ago and didn't remember my password. There was no option for a password reset.
Created a new account--was surprised I was allowed to use the same email. Maybe that's the source of my current woes.
Even though same email, C8 hub didn't see any of the cloud back-ups. And, I could not figure a way to use a local back-up file. Always ended up "Starting Over" (gosh, so many times!).
Finally, brought the old C7 hub up and found a place to get a password reset. Did the reset, then went back to the C8 and use it to login.
Tried doing the resto, but I've been getting a spin box for 15 - 20 minutes. Should it take that long? If not, what should I do next? (I closed the web page, came back in, but still just spinning)
First try just going to another page like /logs or something see if that loads.
If still stuck, go to diagnostic tool and first, do download latest firmware, then restore prior version and update to current firmware. Then do a soft-reset after it reboots (from diagnostic tool).
I dont think it lets you do that, unless maybe your old account was from a "social media" link like google login. I think they stopped using that for new accounts and there was some sort of migration process. So maybe the old one was a social link and the new would be a direct account.
Only other thing I can think of, is are you sure the C-8 can get online to the internet?
You can try setting it up as a new hub, and then go to the network settings > tools. Try to ping something like cloud.hubitat.com and/or some other random web page URL. This will test the DNS and internet connectivity.
Besides that it sounds like maybe you have two separate accounts, possibly due to what I described above with the social accounts.