Table of Contents is duplicated

Somehow the table of content appear twice in two different versions (one which only have the standard H1, H2, H3, … headers; and one which also includes some additional headers generated by another plugin).

Both table of contents have the same class name, so I can’t use CSS to make one of them disappear.

I have a test site where I don’t have this issue, so it’s only in production.

I’m looking for a way to either prevent this duplicated table from being generated or a workaround to simply hide it.