Can anyone help diagnose and treat my tall, ten-year-old plumeria trees? The main trunk and branches have deep wounds that appear to start as dry, splitting bark.

My beloved plumeria began as two small sticks , which sprouted for me and faithfully bloom year after year. I keep them indoors from mid-Sept. through late May because oof Minnesota's terrible winters. I treat them lovingly all winter long as they fight spider mites and dryness. Usually they thrive once they are taken outdoors to fresh air and saunshine. BUT not this year - they have very tiny leaves and wounds all over their branches. THANK YOU.