It's my understanding that rapid bloom drop is usually because of changes in temperature that affect the plant.
I'm not sure what is going on but I had a grower tell me that when you use lava in the mix, you have to make sure that is clean and does not have too many mineral in it, so its better to wash the medium before using it.
My mother had an orchid on a large lava rock, and she had to keep sitting on water. (orchid was killed by my sister, when my mother went on vacation, she use tap water, instead of distil water). Too many minerals on the rock.
Sorry can't be of much help, I'll give you a bump