Why does one of my staff get less efficient much faster than the others?

Game Dev Tycoon
#1

One staff member (Jane Lean, in case names are tied to something) always starts to lose efficiency MUCH sooner than the others when I am developing a game, even if she has just returned from vacation.

Is this related to one of her stats? I don’t see a significant difference in her skills & research or speed from the others.

If not stats, what is causing Jane to lose efficiency before everyone else?

#2

Do you always sent Jane on vacation when her efficiency bars shows or do you wait until the others are also ready to go on vacation?

#3

Usually I send everyone at once.

Weirdly, a few hours after I posted this she stopped having the low efficiency. Don’t know what changed.