I ran a quick rbd sim with packed objects, unfortunately when I look at the impact points attributes, all the *primuv attribute values are always 0.0.
is there a way to retrieve those uv values differently?

Cheers

Since the Bullet solver doesn't directly use the source geometry for collision detection, the impact points might not actually be on the surface of the source geometry (for example, a convex hull collision shape could be used with geometry that is concave). Furthermore, recording UV coordinates for an impact against a packed primitive would be much more complex, since you would need to record the primitive number for every level of nesting (packed primitives can be nested arbitrarily deep).

You may want to consider using the Ray SOP to project the impact points onto the (unpacked) geometry and find the UV coordinates there.

I am already using the ray sop, I was hoping to get that information from my sims, but it makes sense that it would be complex to get the correct data.
btw, why are the concave collisions so bad. 2 concave objects colliding with each other will always intersect so much that it makes it useless.