I don't understand your posting. You seem to imply that archive.org is actively deleting these pages for some reason? How do you know they are "missing"? Were those links once showing the correct page? Else, how do you know there wasn't a server failure on the Slate Star Codex server which caused the ArchiveBot crawler to not record the expected page?

Note that all of those pages have 100+ copies saved, and most of them show content matching the current page.

334 captures for the title link - https://web.archive.org/web/*/https://slatestarcodex.com/201...

105 captures for the first comment link - https://web.archive.org/web/*/https://slatestarcodex.com/201...

183 captures for the second comment link - https://web.archive.org/web/*/https://slatestarcodex.com/201...

The second of these three shows a capture of an error message from Slate Star Codex ("This is somewhat embarrassing, isn’t it?"). The other two show a capture of a 404 error. This suggests that the error is not on the archive.org side, else, why the different error messages?

The common theme is the failure captures were all about the same time, relatively recently.

Perhaps there was a server failure at the Slate Star Codex site which prevented the ArchiveBot crawler from capturing those pages at those time?