not sure what the problem is but it does seem to be happening in the veg stage and once your lower branches are dead there really is no bringing them back so it looks like you may be flowering palm trees for awhile.
but would suggest you try some different things on a fresh rooted clone or seedling to see if you can correct the problem seeing how it affects the lower part of the plant it may be due to a p or k deficiency alot of your leaves seem small and not nearly as big as they should be and if your not regulary using big bloom in the veg state also you should start along with your fish emulsion you could also try different soil.