Well that's just... terrible UX. Surely there's a setting to enable it again?

> still 404s 80% of the time... looks like a similar problem that Twitter has been having for months (sometimes it says "content is not available to you" unless you refresh).

Sounds to me like a CDN problem in both cases. Content not propagating and possibly not being cached correctly at the endpoint you're trying to use until you refresh a few times.

Just a guess mind, but a relatively informed one since I've had similar issues on my own sites that usually require CDN cache invalidation to fix.

Could you maybe have accidentally removed it in the Customize menu?