Finally resolved this issue.
Root cause is the imported data had an invalid IP address, where one of the fields had a leading zero.
Instead of 10.100.20.9, the entry had 10.100.20.09
If this line was removed from the import data, all other imports were successful.
When the invalid IP was attempted to be imported, Clearpass fails to authenticate all VC's. There is nothing in the Access Tracker.
Resolution is to delete the device that was imported wrong and reboot CPPM.