The initial damage from stepping on the Flarecore ability by the Echo of Jaina in End Times Timewalking is improperly scaled. It kills anyone trying to properly do the mechanic.
This is an ongoing issue from years of Timewalking that has been seemingly ignored by the Blizzard staff.
2021 Bug Report post Jaina's Flarecore in End Time TWing is Insta-Killing (Definitely Not Intended)
2022 Bug Report post Timewalking Jaina Flarecore Bugged / Overtuned
Hopefully it will be addressed by the time Cata TW comes around again.