Module not found in project

When using a module in my project, it is saying that “Module ‘xx’ not found in project”. But another module which sits in the same directory can be found with no problem. And their .mod files have all been generated. I wonder why this happens.

The undescore beneath “math_lib” tells that “Module ‘math_lib’ not found in project”, while module “mytest” is OK.

And the mod directory has been included in the fortran.linter.includePaths