I'm using COMSOL Multiphysics (equation-based modelling module - weak form PDE) in order to solve a system of PDE using Discontinuous Galerkin.

When I add weak contributions on mesh boundaries (which is necessary in order to make DG work), an error occurs at solver level:

"Error in multiphysics compilation. Unsupported union between ordinary selection and internal selection on mesh"

Has anybody any idea on what is the problem?

Thank you in advance.