Yesterday I did like 8 runs of Cistern of Slaughter in Mayhem 2…
I kept dying on round 2…
I found 0 legendary…
Today I am at my 2nd attempt, just completed Round 2 for the first time (hooray) (was careful to not kill myself with Amara’s elemental effect haha) and… found 3 legendaries already?! 
What (was or is) going on?!
Just luck of the draw my man 
It’s wildly different luck!