We had a similar problem for the PLY reader. The issue was that colors were assigned per cells in the PLY file but were set on points when data was read. As Yohann mentioned this resulted in discontinuities for the texture coordinates which causes problems similar to what you are seeing. So one thing you can try is to save you data as PLY and then you can toggle between duplicating points at discontinuities or not using
SetDuplicatePointsForFaceTexture (bool)
I do plan to separate that code as a separate filter
https://gitlab.kitware.com/vtk/vtk/-/merge_requests/6079