I cannot say with any certainity with seeing your strokes, but I find that if a player starts getting too topspin happy/loopy, the groundstrokes often fall apart. Get back to basics - "Jump, turn, hit."
Jump - Bounce when you see the ball coming (so you are forward on your toes)
Turn the shoulders (with a simple preparation that takes the racquet head straight back)
Hit through the ball with an easy swing.
Sometime, it even helps to say ("Jump, turn, hit") so you can have a good rythmn