I had a Mango plant that exhibited the same droopy downward curving leaves in mid and late flowering. The next cycle I doubled up on P and K from last week of veg through flower, also added CalMag to the mix starting in veg. Second cycle came out BEAUTIFULLY, I'm going to attach some pics so you can see what I mean. First will be nutrient deficient flowering bud, second will be healthy bud from exact same strain. Turns out it just takes time to dial in the nutes for each strain. Peace and love....