Sample Figma project provided. Export it using Qt Bridge (default setting is all good) and import into Qt Design Studio, then one can see errors:

The reason is that "Frame 1" and "Rectangle 1" are created as Component. And they are used as Instance in "Frame 2" and "Rectangle 2", respectively, and 2 rounded corners are removed, i.e. "Frame 2" and "Rectangle 2" have mixed radius.

The project can be correctly imported if either:
1. No modification to "Frame 1" or "Rectangle 1" when being used as Instance. Or just simple modifications, e.g. changing width and height (but giving different radius is problematic).
2. Do not use them as Component + Instance. A basic frame with mixed radius is all good too.

So in short, Figma Component + Instance + certain "advanced" modification breaks how Qt bridge works.