The prevailing theory is waterlogged roots, especially when combined with cooler temps.

Two growers in Thailand mentioned treated their tree's with fungicide but with all the hot rain they have been getting the are fighting rot also. I just bought a moisture meter. An other member suggested it since I am fairly new and learning what the trees need for my area.

waterlogged causes rot, soil mixture causes rot, over watering causes rot but it depends on your weather. i drench my plants almost everyday and they are fine and loving it. and dont over water if your weather is cold