Get 401 error from authenticated Nuget feed following upgrade to 9.1.5

Hi,

I have just upgraded TC to 9.1.5 (from 8.1.5) and am getting a 401 unauthorised error when I try to download a package from the authenticated internal TeamCity Nuget server.  I am using Octopus as the deployment tool but get the same issue when attempting to download the package with Visual Studio

When I enable guest access and use the unauthenticated feed it works OK - but I'd prefer to use the authenticated feed.

We are using LDAP authentication and there is no problem logging into TC.

Does anyone have any thoughts or suggestions?