I have a build pipeline set up to create Nuget packages and publish them to a feed in artifacts.
I was able to use the feed successfully.
However when I ran the pipeline again, causing the packages to publish again I am not able to update the consuming project successfully.
Even though I can see the correct new version number in the Package Manager (Visual Studio -> Tools-> Nuget Package Manager -> Manage Nuget Packages for solution)
When I click install I get an error
Package '<mypackagename with version number>' is not found in the following primary source
<correct feed nuget/v3/index.json> Please verify all your online package sources are available (OR) package id, version are specified correctly.
After 4 hours struggle I found solution here https://www.grapecity.com/componentone/docs/uwp/online-getting-started/config-nugetpackage.html
Tools > Options > NuGet Package Manager > Package Sources. > Click add button and add following one by one...
nuget.org https://www.nuget.org/api/v2/
GrapeCity
http://nuget.grapecity.com/nuget

Restarting Visual Studio 2019 Community fixed the issue for me.
In my case there was a private network folderbased nuget repository listed in my sources. And at the moment it was not available. I unchecked it in "Tools->Options->NuGet Package Manager->Package Sources" and the whole thing started to work
This is caused by caching. If you don't want to wait like the above answer suggested, just clear Nuget caches by going to Tools -> Options -> Nuget -> General and click on the "Clear All Nuget Cache(s)" button.
You have to check your package source I think the default is
Microsoft Visual Studio Offline Packages
So, you can change that to "All".
I waited another 5 minutes and the problem went away. Maybe the version shows before the publishing is complete.