yeah, this is called "cancellation." Autovacuum is very polite and tries to let go of a lock when there's a conflict. So it lets go, over and over, until it triggers a heuristic deciding "no, not succeeding in this session could be dangerous!" and then people begin to notice it.
Last I checked (....a few years ago, so things may have changed,) the theory of autovacuum heuristics may not have changed much since the turn of the millennium, they're probably about due.