The link to the IG (Package Homepage) from https://registry.fhir.org/package/hl7.fhir.us.core%7C4.0.0 is dead , linking to http://hl7.org/fhir/us/core/STU4.0.0 instead of http://hl7.org/fhir/us/core/STU4/.

This URL is taken from the package manifest ([hl7.fhir.us.core | package/package.json - SIMPLIFIER.NET|https://simplifier.net/packages/hl7.fhir.us.core/4.0.0/files/384974]) and will require bringing out a new package version to fix.