Have observed a few cases like this aswell sometimes recurring. It seems that a healthy sign of a cluster of roots above pot/ media reach a certain length 0.5" to 1" then brown tips and die off. Two answers I recieved 1-not enough humidity and 2- fert too strong with miracle grow type blue ferts being possibilities also. My humidity 60 - 70 % and use specialist orchid fert with low nutrient content npk. Plus media gets flushed out.A mystery and a pain>..........bump! any other theories/ opinions out there?