i can tell you right now that this is a problem with new items not getting added into the category, but the ones that were already in the category are still in it, if that makes sense? like if you go to the category page you might see 5 of the item there, and 5 of the item on the "no category" page, for a total of 10 in the gallery.
i actually thought i'd fixed it a few days ago, but i was apparently wrong.. right now i'm hoping to both a. fix this and b. make it retroactive (which should definitely be doable since the categories are still there on the earlier items), though the retroactivity might require you to click a "fix my categories" link or something. hopefully will have something by early next week!
This has been fixed going forward, and in your galleries you should now see a link that will let you fix it for existing items at the top of the page.
https://subeta.net/user_shops.php/mine/SHOPID GOES HERE/fix_categories
i forgot all about queued items, sorry!