If the enemy used a clearing debuffs mystery, like Han's or Breeze Dancer's sand dust or Temari GNW's one then you are no more immune.

if you use the mystery in a certain moment and after you used it, for example, your enemy han casts his mystery, then he clears the immunity and the shields the mystery grants exactly like it does with lightning armor, root of warrior, etc...

yep, overall if we think that a theoretically equal mystery effect like Bee SST's yo, once is cleared, does no more grant the 2nd standard attack.

They say the reason is that Lightning Armor actually modifies the standard attack itself because is coded in an old way since has always been so, but it's a pretty * justification, imho.