Subaru Forester 2.5 2010 warning light showing

Few days back i was driving and i heard a strange sound suddenly coming from the car. when i stopped and opened the hood i noticed that Alternator belt had snapped (image https://ibb.co/ccVfHv) since i was on the highway i drove car for few kilometers & stopped at a safe place and got belt replaced on stop by mobile mechanic team.

By that time battery was completely drained and i had to jump start the car.

It worked smoothly on highway but i noticed that while car stops or slows down at signal (redlight) it seems to loose power but car doesnt shut off. i also noticed car engine turn off while reversing (this happened only twice in few days)
Today i noticed  warning light showing up for half a second  when i stop at parking area (https://ibb.co/bPVaja) and light goes off when completly when i turn off the AC.

I started having these problem after changing the Alternator belt. what could be the cause of this problem as i can sense something but don't know what it could be