I have following solution structure:

ClassLibrary1 (classic net46)
somefolder\
    ClassLibrary7
        \ClassLibrary7 (core net46)

ClassLibrary7 has project reference for ClassLibrary1 in the form that specify Guid:

    <ProjectReference Include="..\..\..\ClassLibrary1\ClassLibrary1.csproj">
      <Project>{2684d895-d7ce-4b24-a29e-caed2291e2ea}</Project>
      <Name>ClassLibrary1</Name>
   </ProjectReference>

Build fails both from VS and from command line saying that

ClassLibrary7.csproj (ReportAssetsLogMessages target) error NU1105: Unable to find project information for 'c:\users\antonpis \source\ClassLibrary1\ClassLibrary1.csproj'. The project file may be invalid or missing targets required for restore.

Classic csproj would work in this case (VS however showed a warning but built fine) both in VS and command line (command line did not have warnings)