Traction alopecia
Traction alopecia is a common problem with Afro hair styling although it can occur with any type of hair. Essentially, traction in braiding, tight pony tails or even overly tight hair curlers cause damage to the hair follicle. It is like slowly plucking out the hair bulb and even just once in this type of hairstyle, can be enough to permanently stop the hair growing.
See the following articles for more info:
http://news.bbc.co.uk/1/hi/health/6961935.stm
https://www.refinery29.com/en-gb/2018/09/208967/alopecia-hair-loss
https://www.bbc.co.uk/bbcthree/article/361f113b-7edd-4589-8d2f-f1292537e1ba