During the Halkias boss fight, refracted sinlight beams do not match up visually to the actual beam. Standing in between of the visual beams causes damage. I would include link to a video, but apparently this forum does not allow me to submit links.
The common thing when this seems to happen, is that groups have rogue(s). My friends haven’t had this happen in other groups where there weren’t any rogues.
This issue appeared after mythic+ dungeons were released. It did not happen in normal mythic dungeon. Possibly related is the 23. November hotfix “The damage from Refracted Sinlight should now properly align with the beam’s visual effect.”