Viewport Matcap is black

Sorry for my English, I use the Google translator.
I have a problem. Mattsap works fine on all objects, but on object does not work correctly. On tank treads matkap is not working properly.
Watch the video
https://www.youtube.com/watch?v=1V1D-00efxE

So where is your blend file to look at rather than just some video that doesn’t tell all the story.

Is that track an array along a curve ? If so are you selecting the curve or the track. If you select the curve it obviously won’t show up as a matcap

Also please use the appropriate forum for support questions. You may find your problem important but what is this to do with blender discussion ?

Moved to Support / Basics & Interface

how add file?

example

how add file?

my example