with Tarev, plumerias don't like wet feet. Wet soil and cold nights is not a great combination. When my temps goes below 50's I stop watering my plumerias and let them proceed to dormancy. If there is still a leaf or two, I mist the stem and the topsoil just a little bit and let the soil thoroughly dry before misting again. (Lifting the pot is the best indication, if soil is dry the pots are light.)
Also I would watch closely the cuttings that are getting soft and keep them on the dry side. My well rooted cuttings (with blooms) don't get soft at all.