Kind of slapped together
Join Date: Jan 2010
Location: Bossier City, LA
Two good possibilities. Well, three.
1) Hinge pins failing causing it to not line up at the striker bolt. There's articles here on how to replace the hinge pins.
2) Striker bolt itself has slipped out of alignment (not likely, but still.) Or the plastic covering is missing.
3) Where the striker bolt mounts has cracked, misaligning the striker bolt.
For NOW, you can adjust the striker bolt if necessary. But I'd be looking hard at the hinge pins.