NuGet Warning NU1503
Skipping restore for project 'c:\a.csproj'. The project file may be invalid or missing targets required for restore.
Issue
A dependency project doesn't import NuGet's restore targets. This is similar to NU1105 but here the project is skipped and ignored instead of causing all of restore to fail. In complex solutions there are often other types of projects that may not support restore.
Solution
This can happen for projects that do not import common props/targets which automatically import restore. If the project doesn't need to be restored this can be ignored. Otherwise, edit the affected project to add targets for restore.