Hello, I upgraded to High Sierra 10.13.2 (17C88) and XCode 9.2 (9C40b). The problem is now gone. I can create 4-vectors, VectorParameters and TextureSampler2D parameters.
I am unblocked. However, I would like to give a piece of advice. In my opinion it would be highly desirable for your QA team to have access to at least one Sierra machine, or in general to have access to one (Current version - 1) machine at all times. Apple historically has supported XCode on Current Release + Current Release Minus One, so it will not be unusual for developers to be running Current Release Minus One versions.