Other than pump wear due to no servicing as discussed by email then I doubt the unit is at fault, they are pretty bullet proof
I have given some suggestions by email, please go through these to rule out unit issue, but as said above other than lack of servicing which can lead to the unit dosing less than dialled in, i dont see any issues, but I will continue to support you via email.
One last thing, pump calibration is important - make sure you have calibrated the unit recently as per instruction manual.