I have a Plumeria which I grow indoors. This is the first time that it has ever bloomed. Before the bud gets to fully open, it drops off. I did notice that there is a sticky black residue at the base of the leaves. I have another Plumeria close by and there is no black residue on it. The last time that one bloomed was in 2018.

Getting a plumeria to bloom indoors at all is a feat. You should congratulate yourself