[GAMEPLAY] Baron Buff not going out to minions

Baron buff was on myself and my team. I noticed minions were not getting buffed even when standing next to them. Team mate reported the same thing. It did sometimes buff some of the minions.

I do not know how to recreate this. We did an early Baron, that's all I can tell you. Maybe just before the 30 min mark.

Only this one time did I notice it. I played as Swain, team mate was Rengar (maybe something to do with Swain ult and changing forms and Rengar ult turning invisible?) .