Shield toss no longer working?

I'm playing on Steam/PC and inexplicably, my shield toss is just, gone? Usually I hold the right mouse button to charge, but now my Rook just goes into defensive stance and chills there.  I've tried quitting and restarting the game, loading earlier saves, changing the button mapping - no dice. I need that shield toss to break blight boils and venatori crystals, it's literally keeping me from progressing! Anyone else experiencing this, or have a fix?