I THINK I see what the problem is with idle XP earnings.
Right now all of my active character - Outerworld team and Expeditions team - are all in a Soul Room, except one character. Seven hours have passed and all those who are in a soul room have 7XP, the one who is not has more.
So it would seem that the soul room does not add XP gain from the Soul Room does not add to XP gain from the main Expi feature, it replaces it. It also seems to reset current XP amount upon quitting the game.
I think you just need to find a way for XP to never to be removed, lost or reset, only added. Sounds simple in my mind, but of course I'm not the nerd here.
Well, not THAT kind of nerd ;)
