Plastic debris stuck in shower valve?
I can assure you that is most definitely dip tube debris. If your water is excessively hot it could fail prematurely. If it was installed with heat directly on the water heater nipple the heat could have damaged it, causing it to fall into the tank and now it is falling apart from flopping around the tank and laying up against the heat exchanger if gas, or against the elements if electric. Easy way to tell is to remove the nipple on the cold side of the water heater. If the dip tube isn't there, you know it fell in from installation damage or has fallen apart.