The issue happens only for objects using the "RetopoGroup5" mesh, which get replaced/renamed by a mesh called "Combined mesh (root: scene)". I don't know what is happening in the project that makes this specific mesh to change, but I really don't believe it is related to Curvy Splines.
I tried to remove the objects using that mesh (obj6 instances) then recreating them and it seems to work.
I tried to remove the objects using that mesh (obj6 instances) then recreating them and it seems to work.
Please consider leaving a review for Curvy Splines, this helps immensely. Thank you.