There’s a bug in Halls of Atonement where you can manage to snap a Stoneborn Slasher in to Sigar, the miniboss before the last boss.
Just had this bug happen twice in high keys of HOA and dug through the logs to find the reason. When you teleport to Sigar, you run back towards the previous boss on a different elevation.
You end up right above the Stoneborn Slashers and our frost DK’s Glacial Advance pulled through some 5Head dimensions, snapping the Stoneborn Slasher up to us, killing the healer and DK while evading. Here you can see how it happens. Press play down to the left.
https://www.warcraftlogs.com/reports/TnQdJ9PMg6z4RyZL?fight=47&hostility=1&view=replay&position=1533387