"Mesh is not convex" when importing EDEM Polyhedral Particle Shape

Hello,

EDEM provides the error message "Mesh is not convex" when I import a polyhedral particle shape. I have checked that the mesh is watertight and that all normals point inwards. I have included a screenshot showing the particle shape and I have included the geometry as an STL file. This is a very simple mesh, and therefore, I am unsure what the issue could be. Any advice would be greatly appreciated. Thank you.

Particle Shape