Hi! I wondered if you wouldn't mind advising?

I am completing my dissertation on the impact of harnesses on elbow extension, elbow flexion, shoulder extension and shoulder flexion. I have used a generalised linear mixed effect model.

Followed all the coding but for some reason in the test results it is missing one harness, which is the chest plate. And I can't work out why?

It's the same one missing from all 4 tests. But when I do descriptives it is there? I can't work out why it's missing, any advice would be greatly appreciated!