“Post name” permalink option making some pages 404

I’m having an issue with some of my pages 404ing the the “post name” permalink option selected. If i change it to “plain” the pages suddenly work, but stop working when i switch back. Pages that have a parent seem to work fine, but the parent pages themselves 404. The site in question is part of a multisite and the other site on the network doesn’t have this issue, so i don’t think it’s a server problem (but i’m open to being told i’m wrong). What can be causing this?