When importing a new server from a cpanel backup and the following conditions are met you a get a error.
You import a cpanel backup and assign the admin/username and that same admin/username has a alias already from cpanel you will get a migration pertaining to virtusertable.
Error for me was:
Copying email aliases ..
Failed to migrate virtual server : makemap failed :
makemap: /etc/mail/virtusertable: line 10: key username/admin@public-integrity.org: duplicate key
As you notice the makemap failed because the new virtual server admin/username already had a alias from cpanel which I didn't know they already had.
Temp Solution:
Ask before making a admin/username if they already have a alias with the same name.
I don't know if the migration went all the way through still but it looks like it didn't since I had to manually move the cpanel website path to the path I use in VM.