Device: Gaming Pc Asus (ROG) \ Hp pc

OS: Windows 10

WTR (way to reproduce an issue):

Step 1: Go to Classic Arena

Step 2: select a team with Master Butcher in (in my build set Master butcher have item with shield)

Step 3: wait on attack (global) of one enemy and see the effect of heat attack.

Description:

Master Butcher passive "heat exchange" say "When attacked, heals all allies equal to the amount of damage taken. [Does not work against Bosses]. ", but in good amount of cases it not work correctly: in some cases passive enter (cool down start) but heal is "0" for all, in other cases passive is not used and in other case passive enter. 

Is screen below you can see the damage on MB, but heal is "0" for all (except kael because he have vampire set):

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