The only non-standard code that runs on some of these categories is the discourse-category-sidebars theme component.
This is the plugin list:
The only non-standard plugin (except for whos-online) is the SealabsOnebox which just produces onebox previews for a website that doesn’t support oEmbed - I can’t think that it can interfere with category loading (especially specific category loading).
Thanks for the tip, I will to try update the slugs and I will update this topic with the results.