In the direction of traction (opposite of your movie) your the belt lost 3 teeth, then 6, then 12 or 13. I think the (32T) transmission sprocket is more likely to shear the teeth if the belt got loose or if you had a cramp in the left hand
my belt issues -- stripped teeth -- belt replaced -- less than 1k later belt snapped -- new belt pulled out of the garage hit it hard belt snapped -- new belt new rear pulley (under warranty) no issues since then --- check the pulley