Bug with groupies?

Anyone notice that groupies only heals half the time? I thought it was because they were out of range, but i can be standing next to someone, use guitar solo and they only get rockstar buff.

Groupies and Rockstar have the same range so if they get Rockstar they should also get the healing, but sometimes i don't see it heal them. Also if I'm standing next to multiple people like 3 or so only 1 or 2 of them will get groupies. It seems like it's completely random on who gets it too.