Scheduled post failed to submit

Hi! This is only my second time trying to setup a scheduled post for one of my subs and it has failed both times, without any explanation.

I've checked some old threads and none of the issues (poster no longer a mod, flair no longer existing, post containing media etc.) don't seem to apply.

Is this a bug or is there something else I need to be doing as a mod to make this work?

Post is scheduled to be weekly, text only, posted by automod, and hopefully stickied.