Okay, I've been off photographing the stamp that is keeping me awake nights (not really, but it's been annoying me during the day).
From bottom to top: The stamp itself. Then detail on the leaves as it stamps on plain WW cardstock (some desultory Prisma coloring on one of the flowers, ignore it). Then those same leaves stamped on WC paper using I don't remember which inks, but it doesn't matter because they all did a poor job. I tried Memento, India Ink, Palette Noir and Ranger Archival black.
My watercolor paper is 90 lb. Canson cold press and I didn't think it was terribly rough. The 140 lb. I have is rougher so I didn't even bother trying. I can stamp this stamp on plain cardstock and it stamps pretty much perfectly every time.
A paper issue? I'm thinking so.