.NET standard dll library added to the PCL (an issue)

My partner has added a netstandard1.1 nuget package library to a PCL

Now I can't compile as usually. I've got an error, using the msbuild on Linux:

error CS0246: The type or namespace name could not be found (are you missing a using directive or an assembly reference?)

But, monodevelop doesn't show an error in the similar project.

Macincloud/Mac also doesn't show any errors in the Visual Studio.

I've tried to use the xbuild instead of the msbuild - and it works.

But, now the VSCode doesn't see (intellisense) that netstandard1.1 library (its methods).

Monodevelop works (I am using version 5.10; I don't use the flatpak, because it didn't work for Xamarin.Forms last time that I've tried to use it, but an ordinary Debian 9 Stretch package).

On many sites people write that we should not add the .NET Standard library to the PCL, but using another apporach.

P.S. Interesting that VSCode may work with .NET Standard library + Xamarin.Forms if I use
dotnet restore
and if I create it from the ground (but not transforming the PCL to .NET Standard).