See here. stall_selected means the instruction was selected (its not actually a stall). stall_wait is an intentional act by the machine that acknowledges that a pipeline is not available. The approximate equal weighting of those two suggests that there may be a pipeline that can only accept a new instruction every 2 clocks.
To a first order approximation, I don’t think STG.E has anything to do with FMAHeavy pipe.