Hi,
I got this from the team:
"Problem is that the proxy mesh doesn't start at 0 along Z axis, the stem goes into negative values."
To solve this select all faces of proxy mesh (in sub-object mode) and move them up such that the stem starts at 0 then the artifact goes away.
This has been fixed for current versions of Ornatrix but since you are using V4 this workaround should work for you. Let me know if that helps.
Jeordanis Figuereo (Product Designer. EPHERE Inc.)