What is eating my Persian Shield?

I had 2 of these in separate pots on my SW Houston area (9b) patio and they were doing wonderfully until last week when something decided to consume the leaves.

There are no visible insects or caterpillars on the plants yet over the past few days one plant's leaves have disappeared entirely the other has only the top half dozen remaining when just a week ago was lush with foliage.

The leaves are disappearing from the bottom of the plant upwards. They have not fallen off as there are none to be found anywhere. They aren't any partially eaten leaves either. It is an all or nothing disappearance.

The remaining leaves appear completely healthy and full colored.

None of my other patio plants have this issue. Deer are ruled out since there are none in the area and the plant is on a stand 3' above the ground so rabbits are out too.

Ideas?