Did you refinish the door in a different location than where the cabinet is? It is possible the door picked up some moisture and changed shape a bit. Or you applied sealer and finish when it was humid and the door wasn't fully dried.

If the door doesn't straighten out, you can always remove the finish and start over. No big deal. If, after that, it doesn't return to a fit, get back here and someone here will have some ideas. What type of finish is on the piece?

Did you finish both sides of the door?

Doors can warp rather badly if both sides are not finished identically (same finish, same number of coats).

First off, Thanks for responding. Cabinet doors were sanded and stored in the basement over last winter, while the cabinet itself sat in the garage. But everything was painted in the same location with latex kitchen and bath paint. Same number of coats of paint for both sides of doors. So if I remove the paint from this one door would I need to apply some moisture, lay flat and hope that it will reshape itself? Willing to try anything at this point.

Water-based finishes introduce a tremendous amount of moisture into wood. The antique cabinet was extremely dry prior to refinishing.

Leaving the doors off and in a different location for the winter was a bad idea.

My advice is to remove the warped door. Lay it flat on the workbench on top of a heating pad, concave side-up. Turn the heating pad on, and check it every couple of hours.