What's wrong with my refrigerator?

The problem is that the door no longer closes itself. For most of the time we’ve had it, if you gave the door a little momentum, it would finish the job itself. From some door positions, you didn’t even have to provide a push for it to close itself.

We haven’t moved it or repositioned it in any way. It is not overly full.

If you have any good ideas about how to get the door to close itself again, I’d appreciate it.