Thanks all for the replies! Yeah, I live in a condo facing south, so usually by 2PM the mango tree is in shade, but it does get good full sunlight for 4-5 hours.
I'm not feeding it with anything special, just fish emulsion and liquid bone meal, and it was at half strength and AFTER the new leaves have already grown pretty big.
Before that I've been just watering it with distilled water, with a few drops of liquid kelp.
I've never sprayed anything on the leaves except distilled water when I first got it in the mail.