Phoebe bug with Blade Sweep?

One thing I like about phoebe is that she can combo her basic attack and true strike by just holding RT and LT (Im on Xbox), but when I get her mutation Blade Sweep most of the time it will work but quite a lot it just uses the basic true strike without the sweep while using RT and LT at the same time. Is this a bug? If so please look into it as if the mutation doesnt work then what is the point in taking it?

Is “Blade Sweep” the one that makes Pheobe strike an additional time when using the secondary melee attack? If so, I’ve also noticed that it only seems to work sometimes? Are you supposed to mash the secondary melee button so that she does the additional strike or what?

Blade Sweep is similar to that upgrade, its the mutation of that level, both do pretty much the same thing and have the same bug I think