I just spent a lot of time trying to troubleshoot why packages wouldn't restore on my CI/CD server.
It turned out to be cause by the NuGet cache.
TLDR: Clear the NuGet cache with the following command. Note: You'll need the NuGet.exe. Command:
nuget locals all -clear
I was getting an error saying
C:\Program Files\dotnet\sdk\2.1.403\NuGet.targets(114,5): error NU5000: Nuspec file does not exist in package. which didn't make sense since this worked fine on my workstation.
They all gave the error which lead me to try to clear the cache. I used the command above and the issue was fixed.
Note: I don't believe the specific package had anything to do with it. It was just a symptom of a larger problem.