Check the bottom latch that keeps it closed; I bet it broke.
They mount the latch on the bottom of the front face and the corresponding receiver underneath the drawer (remove the drawer and you'll see it--remove the drawer by pushing down/up on the two black plastic pieces that appear on the rails when you extend the drawer out as far as it goes. One piece will be towards the bottom, slide it up. The other will be towards the top, slide it down and pull the drawer all the way out.)
They are held in with
these latches (Amazon).
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