After upgrading to 10.13.5 with latest Nvidia drivers the problem persists. Any idea if I could do anything else? Would 2.8 use a newer version? I guess EEVEE would be even better anyway for that type of shadings.

I just checked the project using another Windows drive that I had around and it seems to be working fine. So I guess the problem is as you said with the OpenGL in my OSX version or something. Will update my system as there is a new one and see if the new drivers solve it. Any idea about what I could do in the case that would not solve it?

I just checked the file using another iMac and the Matcap looks correctly in Material shading. OSX 10.10.5 with Ati Radeon HD 2400 XT. I was wondering if this has to do with Nvidia drivers as you said. Will check the other person graphics card brand as he reported not working on Windows.

The project as stated was tested by another user using a PC on windows and he had the same result while he could have the right result using a Macintosh. I was hoping for you or someone else to download the file and test if you could replicate the problem. My graphics card is up to date and I never had any problem visualizing everything as the way things should look like.