Too new to comment on what's going on and how to remedy it. No one has responded and might be because of plants being dormant, subsequently not as much participation here. But hang in there- an expert will help out eventually. :)

Hi yv would help to know where you are but a obtuse must be kept warm never let it get cold most people that have obtuse have trouble with black tip in cold weather my Singapore obtuse bloomed the first year after it rooted and then went 2 years befour it bloomed again mine keeps its leaves year around but it never gets below 65 in the greenhouse

Roger

My experience with Plumeria obtusa is limited to Dwarf Singapore Pink, so I can only tell you what I've learned from my time with it. For one, it doesn't go dormant like rubras do. My plants need warmth and water year round, as well as light. One of my two is in bloom right now and gets watered every other day, because otherwise the flowers droop. The temperature in their room (a nook in the kitchen) varies between the high 50's to high 60's.