ADXL335 axis out of spec


we are using the ADXL335 in our product to measure angle of an arm.

We are using only the Z and Y axis.

We have the devices loaded onto a flex PCB in batches of 1000 by our Chinese manufacturer.

We are using 2.5V as the power supply. With 0g the output is expected to be 1.25V and vary up to +250mV and -250mV of this value when rotating through 360 degrees and incurring +1g to-1g.

However we are experiencing around 10% of the sensors with axis values outside of this range. Some a long way out. This causes our firmware to error and we are not able to accurately determine the angle.

We have studied the data sheet and it does provide max and min tolerance vales, but the faulty sensor axis values are still  outside this range.

Can you comment on what may be the problem. Could this be a manufacturing issue. Could they be damaged? OR could they be second sourced non-original parts?

Thanks for you time,