Welcome to NGA, 84Brian. Very likely. Stem rot causes the decaying of the inner layers of the plumeria stem. The plumeria stem then becomes/feels soft and squishy as the inside rots away. This disease usually occurs while trying to root cuttings, during winter storage, because of winter injuries or when over-watering the soil. If the pin prick test shows brown ooze or no signs of white latex, I take either as a sign of stem rot. Sorry for the bad news. :o(
