Why are supposedly ActivityPub-federated Discourse threads inaccessible via external AP clients?

Support
1

Example

If I enter https://meta.discourse.org/t/uris-to-the-origin-of-a-thread-that-has-since-been-merged-should-503-to-the-merged-comment/342417?u=rokejulianlockhart (or https://meta.discourse.org/ap/object/bc8f042ccca5ef56734c5f2460aa45cc) [1] into mastodon.social/search, it 404s: [2] [3]

The image shows a web browser displaying Mastodon, a Twitter-like microblogging platform interface, where a user can search for content or post updates. (Captioned by AI)
The image shows a web browser displaying Mastodon, a Twitter-like microblogging platform interface, where a user can search for content or post updates. (Captioned by AI)1280×680 87.8 KB

If this isn’t Discourse’s fault, I’ll take this to Mastodon. However, most other AP platforms that I’ve tried (that I’ve expected to work) have worked.

  1. https://meta.discourse.org/t/uris-to-the-origin-of-a-thread-that-has-since-been-merged-should-503-to-the-merged-comment/342417?u=rokejulianlockhart ↩︎

  2. search?q=https%3A%2F%2Fmeta.discourse.org%2Fap%2Fobject%2Fbc8f042ccca5ef56734c5f2460aa45cc ↩︎

  3. search?q=https%3A%2F%2Fmeta.discourse.org%2Ft%2Furis-to-the-origin-of-a-thread-that-has-since-been-merged-should-503-to-the-merged-comment%2F342417%3Fu%3Drokejulianlockhart ↩︎