Yes, I see this issue consistently with Source Sans 3. Setting the font-weight directly works fine, but encoding it in a style yields unpredictable results.

Have you figured out how to solve this? Having the same issue.

I have dealt with similar issues regarding variable font settings packaged into type styles. Usually the problem has been some sort of font conflict between multiple users. For instance, I tried to create a few styles with non-default OpenType settings enabled for Inter, and there was a strange conflict between the Inter that I didn’t know was installed on my machine and the one Figma provides by default, which caused the fonts to not render according to how I set them in the style definition.

So, I would check to see if you also have a local version of the font that’s giving you trouble installed, and disable that. Your teammates might want to do the same to ensure you are all working with the same version of the font.

We have had similar issues in the past. For us it was like Brian_Saunders, designers seemed to have different versions of the font locally, which had slightly different naming styles, eg Source Code vs Source_Code so every time someone entered the file they would get a missing fonts pop up, change it, and then the next person would do the same, breaking all styles. This happened quite late in one of our projects and ruined next few days trying to re-instate all the styles