I took some recordings this time, I was able to recreate the bug in the latest release.

Here is the furnace recipe book working as I'd expect:

And here's the brewing stand acting a little odd:

From what I can tell this is what's happening:
Toggling the filter on and off updates the recipe list, adding items inside the brewing stand itself.
But opening the brewing stand directly doesn't add the container's items.

Also picking up items while the brewing stand is open doesn't add the filtered items to the list, whether that be from the ground or the brewing stand

Btw, thanks for all the work you do! :)

I noticed in your first gif that your resource pack has something for the mods custom buttons, thats kinda cool

Oh, i found the issue. When you filter and then open the stand directly it does not update the list

Honestly this has really stumped me. The brewing stand is initialised before its inventory is populated..