NuGet Warning NU1603

'PackageA' 4.0.0 depends on 'PackageB' (>= 4.0.0) but 4.0.0 was not found. An approximate best match of 5.0.0 was resolved.

Issue

A package dependency specified a version that could not be found. Typically, the package sources do not contain the expected lower bound version. A higher version was used instead, which differs from what the package was authored against.

This means that restore did not find the best match. Each restore will float downwards trying to find a lower version that can be used. This means that restore goes online to check all sources each time instead of using the packages that already exist in the user package folder.

Solution

If the package expected has not been released then this may be a package authoring error. Contact the package author to resolve the issue. If the package has been released, then check that it's available on the package sources you're using. If using a private source, you may need to update the package on that feed.