“Quote” no showing when selecting text with style changes?

On my forum (https://www.keyboardmaestro.com/), often when I select text in a message, the Quote button does not appear.

I’ve now narrowed it does to when the style changes, so for example, when there is a link or bold or italic text.

I can see on this forum it does not seem to be a problem.

I don’t have a lot of plug ins enabled, just:

image

This is using Safari on the Mac (but again, the Quote option works on this forum so it does not seem ot be just my browser).

Any ideas what might cause that?

If you can’t repro it here, then it’s something specific to your site. What is the discourse-mark plugin doing?