Vammatar the Cruel occasionally afflicts players with two debuffs which always come in pairs: one player gets Corrupt Soul and another player gets Corrupt Body. Judging by the description on the Corrupt Soul tooltip, the idea seems to be that players stay apart until the debuff is close to expiring, but then hug someone with the opposite debuff to avoid getting oneshotted when the debuff expires.
However - and this is the part that seems bugged - the player that gets afflicted with Corrupt Body immediately gets a large number of frost damage hits, each of which is small individually but which taken together (and they all come within the same second) nearly always kill him. This in turn means that players with Corrupt Soul have nobody to hug that could prevent them from being oneshotted at the end of their debuff, and so they die as well.