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This information should be checked by one of the team members, @Linc
On the website itself it could just be an invalid url with how your urls are set up. I found that link on Google search results. If the post wasn't found, it should have displayed a page not found though if I'm not mistaken. Not an error page.
The view for our rich editor error handling (the one referenced here https://docs.vanillaforums.com/help/addons/rich-editor/#why-is-my-published-post-replaced-with-there-was-an-error-rendering-this-rich-post) got misconfigured during some recent refactoring.
PR here https://github.com/vanilla/vanilla/pull/8275