I'll throw this out to the Community while I wait for support:
Migrating from vCenter 6.0 Windows, external PSC to vCenter 6.7 Appliance - external PSC.
The PSCs and one vCenter in our environment upgraded without issue.
One vCenter migration failed after deployment and during configuration of "Content Library Service" with an error message ending in "Name or service not known".
The source vCenter was brought back on-line and re-joined to domain without issue
The second vCenter migration failed prechecks with "Source vCenter Server had duplicate names in a network folder"
I cannot find the KB referenced - 2147547.
And we do not see any duplicate names in networking.
Did you get this issue resolved?