That's what I thought too. The sudden stop is actually two phenomenon compounded. One, the mountain of ice contacts bottom. Two, the video speed changes from ~8x to 1x.

One of the comments said just that. "Grounded near disko bay" iirc.

Another comment said that icebergs melt blow water faster than in the air and that flipping is a fairly common thing to do because the center of gravity changes.