I am not sure but I usually do not like black anything anywhere on a plumeria. But I am puzzled. Did you bring the plant indoors so you could take pictures now under grow lamps or ??? Just wondering. They really like sunny locations unless the heat is extreme like mine in Texas.
Watch out for pests like aphids, mites that bite leaves to suck juices. You may have to look at night. Do not water leaves if you suspect fungal issues. Make sure the pot still drains well, that you water if the soil is dry and try putting them outside (very gradually though).
