I've got an vellum I/O with some simulated grains, which I've connected to an attribute VOP giving it a custom parameter through a noise that I'm animating

However when I plug that into a vellum solver the values of my custom parameter are stuck on frame 1, as if it's not updating the value over time.

Any idea how one might feed data from an attrib VOP into a vellum solver? Or how else one would go about masking grains with a noise within the vellum solver ?

the vellum solver on sop level is only taking information on first frame to sim the constraints over time. If you want to animate the constraints or geometry you have to dive inside the vellum solver which means you are in DOP world now. Here you can feed attributes per frame or subframe(or specific frames) to alter your animation. most likely you can use vellum constraint property node to do most stuff..

hope this helps get you going..