Is this a new BigFix instance? If so, have you successfully deployed MS patches previously?
Does your BigFix server access the Internet via a proxy? If so, have you verified that other sites are gathering as expected? If you’d like, you can DM me to provide a copy of your GatherDB.log from your root BES server.
Do you see any related errors in the BESRelay.log on your root BES server?
As @MDMike indicated, the current version of the Patches for Windows external site is 3,567.
When the BESGatherDB service is operating as expected, you should see something similar to the following in the GatherDB.log from your root BES server.
Mon, 22 Jun 2020 12:28:04 -0400 – Beginning DB import of version 3567 of site Enterprise Security
Mon, 22 Jun 2020 12:31:05 -0400 – Import of version 3567 of site Enterprise Security completed successfully
I hope this helps.