When I do my Plumeria talks (and I do them regularly) I always emphasize that although people want to trim their trees in the fall when they are getting lanky and in the way, it is the worst possible time to take cuttings for propagation purposes. They are about to go dormant. Guess what happens with a dormant stick? Nothing, that's what. So they sat there and simply dehydrated, is my guess.
Having said that, if it was me I would take the ones that are still viable, maybe put them in a bucket of water with a drop of superthrive for a couple of hours, and then re-root in the pure perlite. I would not cut them again, they don't need more stress
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