If the glissen ability procs during a charged PA start to a chain combo, it ends the chain. Game treats your first charged PA as the finisher as well and you get that sweet 7-9 hit chain. Only happens to me when I start a chain with bullet rave, since it has a long animation. Thought it might be user error at first, but its been happening to me all day, most often during Giga fights of course.
Converse with fellow players