Many young players are taught to get in front of the ball or center on the ball. This can create problems at times. They tend to try getting in front of balls in the hole that need to be back handed and they are often fielding routine ground balls on the throwing arm side of their body.
in addition to the suggestions above, make sure you are fielding balls on the move and receiving the ball below your left eye or ear. Those that field ground balls in front of center body or open handed on right side of center will have less up and down glove flexibility and thus they will appear to have hard hands.
That said everything starts with the feet. And every so often balls are hit that will require great instincts and reaction. And sometimes the situation calls for keeping the ball in the infield above all else.
One last thing, most slumps are caused by mental rather than physical issues. This can happen to anyone be it throwing, fielding or hitting.