I recently bought two Yongnuo 568 EX IIs and they're working great! I'm just having one problem in one of the two: when I put the flash in any of the slave modes (Sc, Sn, S1 or S2), the red lights do not blink on it like it does on my other flash. However, the flash is functioning perfectly as a slave, it is just that no red lights blink on it. If it makes any difference, I'm using them with a Canon 600D.
Is the lack of lights a symptom of a problem I'm not aware of, and is there anything I can do about it?