This is normally a font issue I've had the same in Sketch. It's harder than you would think to sync fonts across machines. To verify try it in a web browser with local font loading diabled/uninstalled or switch to a web font neither of you have installed locally.
I've had this same thing happen with a variety of fonts. It's happened between me and other designers like you, but it's also happened with my own files and elements that I've created. Drives me insane it it throws our layouts completely off! I do think there is a serious problem here and not just different versions of a font being installed. We've never had this problem with other design programs like Illustrator.
Guys, don't forget that Figma is using Chrome as a base, so we're talking about Web Font Rendering that is entirely different from Mac to Windows as well as from a browser to another. If it's a web project that will be sent to developers by the end, it won't be a problem as they can fix that in CSS to make sure that all browsers render the font properties correctly. As for the team collaboration, I would suggest using the same browser version, same font family package in TTF or OTF before opening the files, since Figma is on autosave if you open the file for the first time with fucked up fonts it will automatically pick your version and save it.