If everything is public it should work, sounds odd, are you upgraded to latest.
Does this happen on all posts. For example any internal link on your forum fail? What do you all call your Discourse forum? - #34 by debryc
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Does this happen on all posts. For example any internal link on your forum fail? https://meta.discourse.org/t/what-do-you-all-call-your-discourse-forum/160991/34