i've got a coerulea doing the same thing. i've cut off the leaves and the tips where it is cut start to dry up and die. i've used anti-fungals, and been careful watering and no luck, the leaves are slowly dying towards the stem. only a few leaves near the top. i've gone and bought another now just in case it kills the top of my plant. no other plants near it have been affected. it was doing so well at first. i thought originally it had sun burn, but the spot kept getting larger. then another leaf. it is now starting on a 3rd leaf i think. and i have cut 2 leaves back twice trying to get ahead of this infection. no luck. i have not used cinnamon on it, but have used it before with bad luck... i find it can burn plants. i have dipped the plant and it's treefern pot into a very mild bleach solution, no help, no harm.