Exterior Wall - Stacking Fiberglass insulation and Mineral Wool insulation
Vapor barriers are installed on the warm side in winter on walls.
If you leave the vapor barrier in the middle of the insulation envelope, it will trap the moisture in the wall causing mold or dryrot or both.
Vapor travels from a warm environment to a cool environment. When it reaches its dew point it changes from vapor to water. If this occurs in the middle of your wall and can’t dry out, it’ll create mold, dryrot, etc.
If you add insulation, I’d remove the paper vapor barrier (or slice it into a zillion cuts) so the vapor or moisture can travel through the wall space.
This may help:
https://www.energyvanguard.com/blog/75130/What-Happens-When-You-Put-a-Plastic-Vapor-Barrier-in-Your-Wall