Please check the Zigbee again. It sounds like we may have a migration problem bigger than the issue seen with users coming from C5, which we are aware of. Alternatively, do you mind trying to downgrade the C8 to version 2.3.5?
Go to this end point:
HUB.IP/hub/advanced/downloadPlatform/XYZ
Where XYZ = 235 for 2.3.5
Then go to Diagnostic Tool and restore previous version and select 2.3.5.
