Font weights work working on Mac but not PC

So I'm working on an InDesign project, and my school uses Mac. I have the entire Montserrat font family activated, and an important text element is set to the "light" weight. It works fine on the school Macs, and to be clear I am signed into my own personal CC account while doing this. But for whatever reason when I open up the project on my own PC, that particular font weight, as well as two other weights, are not available. I get the missing font dialog box and the weights are displayed as [light] and so on.

What is the meaning of this, and is there a fix?