It sounds like it is going right to seed.
Maybe too much water, too much fertilizer??

It is not unusual for the early buds to shuck off due to extra rain or nutrient uptake. Give it a bit of time, I live in zone 6 and mine are just now forming buds, some have shucked off.

I have had trouble in past years, since it seams the plants look so unhealth for so long I felt I needed to feed them - Big Mistake!. Give them no food, or water lest you want rampant growth, at the expense of flowers.

I find Moonflowers take a while to take off and get those nice large leaves and finally flower.