Yeah, TigerBeetle's blog post goes into more detail here, but in short, the tests that were running in Antithesis (which were remarkably thorough) didn't happen to generate the precise combination of intersecting queries and out-of-order values that were necessary to find the index bug, whereas the Jepsen generator did hit that combination.

There are almost certainly blind spots in the Jepsen test generators too--that's part of why designing different generators is so helpful!