That kind of damage could be caused by a number of things. Too wet soil, too dry soil, heat damage, or high salinity / minerals / fertilizers in the soil.

Mangos are native to monsoonal areas of India, they can take degrees of drought in the dry season (winter) once established, but they will not survive in Saudi Arabia without additional water. As above, it might also be reflected heat damage or the soil condition.

Guys, a pleasant surprise today: one of the trees (the eldest one) grew new leaves ever where

`I hope the other two will do the same thing soon ;-)

Mangos tend to grow in spurts, no growth, and then a lot of new growth. Again, their native climates alternate between the big WET and the big DRY.