Were those new or reset devices? If they were still paired to the c5 then they won’t pair to another hub.
Also, is it plain C8, or Pro?
Did you happen to mess around with it and change Z-wave to Zwave JS before migrating? There seems to be an issue with that if the backup is ZIP and the target hub is switched to Zwave JS already.
Also what about this? The C8 is sensitive to unstable voltage. PoE has been known to cause issues.