We have an internal NuGet package feed (published from TeamCity), and after updating VS2015 NuGet Package Manager as prompted by VS, I can't see any packages in the feed that were published before the NuGet Package Manager update.
I can navigate to the feed URL and see all the expected packages in the resulting xml (proving that the packages do exist on the server), but they do not show up when browsing the internal feed in NuGet Package Manager. Packages published since the update do appear when browsing.
I did not have this problem in VS2015 before this update (now on NuGet Package Manager version 3.4.2). My co-workers using VS2013 are able to see all the packages as expected.