Core projects fail to build when they reference other projects not included to solution

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:

```

{2684d895-d7ce-4b24-a29e-caed2291e2ea}
ClassLibrary1

```

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)