Answer: Sounds like your plants may have become sunburned. This can happen when they are grown under nursery conditions where they are shaded from the hot afternoon sun and then you plant them where they receive full sun. I'd prune away the sickly parts of the plants. As they generate new growth and new leaves, the leaves should be able to tolerate full sunshine. Be sure to water thoroughly and then allow the top inch of soil to dry out before watering thoroughly again.
Best wishes with your potato vine plants!
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