Snipe it's possible the inner lining of the hose is becoming de-laminated and causing your blockage.
To eliminate the hose as a possibility, see if you still have pressure at the pump when flow stops, put a tee there for a pressure gauge, if you don't already have one.
To be clear, this is the only diffuser on the system?
Another possibility is the battery, it's solar right?
To eliminate the battery as a possibility, check your voltage before and after, the flow stops.
