SOURSOP TREE

Question

TREE IS 5 YEAR FRUIT EVERY YEAR. THIS YEAR LOTS OF FLOWERS BUT NO FRUIT.

Answer 1

It could be there were no polinators around, in this case, nitidulid beetles. Also, environmental problems such as too much wind, low humidity, cool weather can affect fruit set.
Here is more:
https://edis.ifas.ufl.edu/pdffiles/MG/MG33000.pdf
https://www.gardeningknowhow.com/edible/fruits/soursop/soursop-tree-care.htm