two possible reasons.
#1: The lower manifold screen has broken. This is very common when companies use cheap botom screens. The company I work for will only use 1 type, see the picture below. This is made in Italy by Pentair, cost a lot more than anyone elses, but considering the importanceof the bottom screen, why would a company try to save $4 on this?
#2: System plumbed in backwards. The top screens(if they are even installed) are not a sturdy as the bottom screen and can fail if the system is plumbed in backwards. The top screen is intended to distribute the water evenly through the bed and to protect the valve during shipping. it will also lessen the potential of media loss in the case of cold water which can cause the bed to over-backwash.
Inspect your plumbing direction first since this is easier than taking the valve off. I believe the Aqua 2 was pretty easy to remove the valve and manifold assembly, but it has been years since I have worked on one in the field.