A fare can only be held while it is valid. If a fare expires in less than 24 hours, so does the hold. There have been previous reports of people getting caught by this, not noticing that a hold expired the same day.

My experience shows that a held fare can go down when repriced using a cheaper fare code, but presumably the opposite should not happen. As long as you are holding a particular fare code, it should remain available at the same price? If not it makes putting a reservation on hold pointless!

Maybe the op's problem related to the closeness to expiry when he tried to make the booking? But it has to be a mistake that AA should acknowledge.