AB tests are still vulnerable to p-hacking-esque things (though usually unintentional). Run enough of them and your p value is gonna come up by chance sometimes.
Observational ones are particularly prone because you can slice and dice the world into near-infinite observation combinations, but people often do that with AB tests too. Shotgun approach, test a bunch of approaches until something works, but if you'd run each of those tests for different significance levels, or for twice as long, or half as long, you could very well see the "working" one fail and a "failing" one work.
Observational ones are particularly prone because you can slice and dice the world into near-infinite observation combinations, but people often do that with AB tests too. Shotgun approach, test a bunch of approaches until something works, but if you'd run each of those tests for different significance levels, or for twice as long, or half as long, you could very well see the "working" one fail and a "failing" one work.