I see it. The problem occurs when editing a reply to a topic, not when editing the topic itself.
This is related to updating to the latest Forums version. The new version allows for inline and threaded replies. While we are not currently enabling threaded replies, it seems the inline reply is used when editing. The inline reply editor is "different" than ones used in other areas of the Community (at least from what I gather from support discussions), which is why the JSL button is not shown.
I have opened a support ticket with the vendor.