I get the following error when I try to useautomodsumm with a template when building matplotlib.
jinja2.exceptions.TemplateAssertionError: no filter named 'underline'. The error happen in the call

template = template_env.get_template(template_name)

on line 511.

I looked into the code and saw that the line

template_env.filters['underline'] = _underline

where in the sphinx generate_autosummary_docs function but not in the generate_automodsumm_docs function.

I added that line and the _underline function and I don't get the error anymore. The result is more as expected but sphinx doesn't render the last level of autosummary files (if that makes any sense, the links on my class pages don't work).