In my experience it was our firewall/proxy that blocked some (but not all) communication with Apple. Has anything changed in your network security recently?

Very odd, I ran in to this problem before. The VPP account password was changed then all I had to do was re-upload token and it was good.

Ours is doing this as of last week and nothing has changed within our environment for at least 6 months. Nor have we changed the VPP password recently. I've tried reuploading the token, but that hasn't fixed it. Has Apple changed something on their end that would cause their communication to partially start getting blocked? Do you have a link for the current URLs that need to be whitelisted concerning Apple services?

*Tried reuploading the token one more time today, and it did fix the problem. For some reason when Jamf upgraded our Cloud instance over the weekend, it caused that token to get expired. I had just updated the token on Thursday of last week trying to fix a very similar issue that we were noticing in our instance.