The Pure Energy spark adds that spawn in pairs as Vexamus is brought through each of his 20% health thresholds are scaling health incorrectly with 11.0.5’s conversion of timewalking to scaling dungeons to the player’s level.
Prior to this change, these sparks always had low enough health that virtually any attack, even a caster’s auto attack, would one-shot them. They instead now scale health to high enough levels that they can no longer be one-shot and aren’t even really worth attacking for the damage buff anymore. At level 74 they had 1.1M health for me, up from the ~10 they probably had prior to the change.
The boss still dies fast, but it was a fun gimmick if one remembered how the fight used to work.