Q.Leaves are disappearing from sweet potato vines
Container Sweet potatoes had luxurious vines. Suddenly the leaves are missing! I have vines with upright stems and NO leaves! Cannot see any insects. Each morning there are a few beautiful green leaves fallen onto the ground around the container. Dug into the soil and found healthy tubers. What’s ailing my plants? (Photos show what appear to be healthy vines, bare stems and leaves found on the ground this morning)

Cabbage Loopers may be the culprit.
This article will help you.
https://www.gardeningknowhow.com/edible/vegetables/cabbage/cabbage-looper-control.htm