I hit that as well, it took a few hours.  if not after that, then there might be a missed step along the way, there are certainly a few picky steps and running through both the video and the docs helped. 

It's OK now, It took some time to populate.

David, in the Legacy feed, the patch catalog was processed on the server side (Patch Server) during subscription and the vendors were populated from that. In the Advanced feed, each device receives the full patch catalog, uses it to scan, determines what patches are applicable to it, then reports those patches back to the server, at which point they are added to the database (including the vendor information) if they don't already exist in the database from another device reporting them. So, in a migration, there are no patch vendors listed in the Patch policy list until after you run patch scans on your devices and they report patches.

This is one of the advantages of the Advanced patch feed. Your console only includes the patches that have been detected on your devices, not all possible patches based on the OS type and version.

Hope this helps explain why you were seeing the vendor list take some time to populate.

-Darrin