[@kai920 Member 16 years, 2 months ago]

Ah, I found the culprit. I had converted from another forum software so the topic_slug and forum_slug columns were empty. Found a script here http://www.simonwheatley.co.uk/2009/07/03/migration-to-bbpress-fix-topic-slugs/

It didn’t convert my forum slugs but that wouldn’t take long to manually input.