Having bug-free code in production is secondary to having a working system. So it's arguably irrelevant that A was the buggy version, because A was also the on

Having bug-free code in production is secondary to having a working system. So it's arguably irrelevant that A was the buggy version, because A was also the only known-good battle-tested version. As a developer who's also in charge of rollouts and has zero QA support I would also rollback in this (admittedly somewhat vague / hypothetical) situation.