[stochaztic]

Here's one way they do it that isn't documented or widely known: an account can get "searchbanned". While your account is searchbanned, your new tweets can't show up in other people's search results unless they follow you. There is no indication when you've been seachbanned or when the ban is lifted, and no documentation on its existence or how to get un-searchbanned. We know because we gather community input on a specific hashtag, and have gotten complaints that specific people's contributions weren't included, because they didn't show up in the search.

Interestingly, we had one person's account whose search results still showed searchbanned tweets. They would not show for that person if they logged out. We also could not find out why that person's account in particular could see them.

[robinson-wall]

Hey, I work on Twitter's search team.

This sounds like a bug we're aware of where an account that goes public -> private we'll reliably purge their tweets from the public index, but if an account goes private -> public sometimes we'll not re-populate the main index correctly.

> we had one person's account whose search results still showed searchbanned tweets

This part doesn't match what I'm describing, but could be explained by the logged in account having access to private tweets in search results that logged out / other accounts do not.

[stochaztic]

Due to both the second part, and that of the 7 accounts that we know this happened to, they messaged us just hours after tweeting that we weren't picking up their tweets, it doesn't sound like a match. The logged-in account also had no history with the accounts in question; we were actively in a call at the same time trying to figure out why that person could see tweets the others couldn't. I'd be happy to discuss details and specific tweets if you want.