I suspect the stage 5 on Kaerok Castle (Hard Mode) has some error on its loot list.

 Stuck on the 7.4 Artifact Challenge: loot a Chest 4* HP% from stage 5 Kaelok Castle on Hard or Brutal.

 I have currently spend more than 1000 energy running that stage (annoying, but not suspicious) AND have looted dozens of 4* Chest of each and every of the other 7 primary stats (ATK, ATK%, DEF, DEF%, ACC, RES, HP). Even i keep one of each on my inventory.

 I am starting to doubt this is merely just bad luck; during farming i get from time to time a 4* chest, but never HP%

 I would like to request to the devs if they could check the loot list for Kaerok Castle stage 5 Hard Mode if the 4* Chest HP% is on that list and with its correct chance.

 Thanks in advance.

 EDIT: This morning i tried to farm it on Brutal Mode. In less than 100 energy, i looted a 4* Chest HP%. Honestly think the loot tables on Stage 5 Hard Mode must be checked.