Why two similar hits, that must deal same damage deal different? what else we don't know about LoL that been hide from players?
Like in this thread:
https://forums.playcontestofchampions.com/en/discussion/158/labyrinth-of-legends-enrage-timer-where-is-the-truth-renew#latest
here the same attack, but one hit didn't get crit. looks like not 20% of armor is ignoring by critical hits.

this happens not only with Hela, this affects LoL champions.