In hdk/common/verif/scripts/generate_sim_file_list.py, at line 48:
if not file_path.endswith('h') and not file_path.endswith('md'):
generated_file_list.append(file_path.replace(cl_dir, '$CL_DIR'))
As .svh and .vh files end with 'h', they are excluded from the simulation compile list top.[sim].f, and can cause sims with .svh/.sh files to not build.