How does the door fit on the other side of the enclosure?
I'm just wondering what is going on with it to have caused that. Wondering if both sides are beginning to lean to the right slightly.
That would also mean that the door isn't perfect on the other end, though.
If that is the case, I would want to look into straightening and stabilizing the enclosure somehow. Because whatever is going on, is probably going to keep happening. The gap will grow and eventually it will be structurally unsound. I wouldn't want it "giving out" while you aren't home.
You could get a level and try to find out where or what is leaning, try to fix that and add support to keep from happening again.