Could be different reasons:
Was there any change in your overnight temperature; or check leaf underside, if there are sucking crawlies there; nutrient deficiency; light deficiency, how often did you water it, was it in shade then put in full sun right away..?

Is it just one leaf or more leaves and buds dropping??

Mine do the same thing, lack of water, too much water but most of all check for those tiny little WHITE FLY. they are hard to see and hard to get rid of

Hi Doris, just came on for a few minutes. I have had a LOT of problem with "white fly" I have a ficus hedge that was denuded by them, then I discovered Bayers 3 in 1. Solved the problem big time. You can't use it on fruits or veggies, but if your white fly is the same as the one that's causing so many problems in the south, that's your answer. Greetings to all.