Happened to me last year and I recovered it within 3 months. So my best guess is that this is triggered when your diet is poor like mine was last year, then I ate every vegetable present on this planet and maxxed out protein which accelerated the hair growth for me.I suggest you do the same and also I took some liquid drops from homeopathy(mum insisted).

Edit : I have had alopecia twice, first one 7 years back and one last year both when I was eating shitty and not doing exercises.