> I don't know why the 1st VACUUM FULL wasn't able to reclaim the same
> amount of space as the 2nd one, but I would guess that it wasn't able to
> get a lock on some table. It could have been autovac if it was doing a
> vacuum at that moment, but it could have been something else too.
Or there was a long running transaction in the background. The oldest
active transaction will place limits on what VACUUM can or cannot
remove.