You might still have that C7 free cloud backup available. I don't know if Hubitat deletes them after some time, but it should still be there. You may be able to restore that right back to the C7, but I think you would need to buy a cloud backup subscription to get access to it. Subscription is pretty cheap. Cloud migration backups show in cloud backups once you buy it.
I bought a subscription to migrate my hub to a warranty hub, so that I did not have to pair devices again, since only a hub upgrade cloud backup restore is free,
You can probably also right now restore the cloud backup from the C7 migration to the C8 Pro, since it should show. How long has it been? It is more than starting from scratch.
The issue may be your hub, though.
tldr; I had a bad hub that was causing my zigbee issues, but all was good at first after migration to the C8 from the C7:
I bought a subscription to cloud migrate my hub to a warranty hub to fix my Zigbee issues:
When I migrated from my C7 to the C8, all was good at first. Until I had to add my first new Zigbee device after owning it for more than a month. I had to fight for a while to get it to connect, even though I had other devices of the same type connected and working fine still from the migration. Rebuilding Zigbee network and then pairing quickly would get them in after a few tries, I finally found.
Then I bought more new devices, and again had issues pairing. Sengled bulbs in this case, I had others of the same type still working great from the migration, but once I finally got those paired they would stop responding within a day, usually hours. The ones I migrated were still happy.
Then my Zigbee network started locking up totally, about every three days. I would find in settings that it just said INITALIZING in Zigbee state. A reboot would get it back up.
Finally, I put in for a Warranty hub, and all my issues were fixed. I took a current cloud backup when the new hub arrived, and then I restored it on the warranty hub and everything was already connected and Zigbee stayed working. Since I used the migrated configuration and didn't start from scratch, I have to think it really was the hub. No issues pairing devices since.
Point is, it may actually be your hub, especially if you have issue pairing new devices. Or just re-pairing a current device if you reset it.