"Cannot resolve symbol" errors with autogenerated GRPC code in obj folder with visual studio

We use the grpc.tools proto compiler for our project. This generates the grpc "*.cs" files in the "obj/Debug/netstandard2.0/" folder of the project. 

It seems like ReSharper for visual studio can't find these files because it gives a lot of "Cannot resolve symbol" errors, but it builds and runs just fine and suspending ReSharper clears the errors. 

I tried clearing cache manually and by the clear cache button but sadly this didn't help.

It used to work, but after a change in the project structure, where the project in question was moved one folder deeper in the structure, it broke.

This problem only occurs for our team in visual studio 2017 and 2019. This problem does not occur for the rider users of our team.

I tried this with the 2019.1.1 and  2019.1.2 EAP version, both with the same result.