I would be looking at the input signal to ensure it is actually 5V - 100% PWM. Then I would be looking at the output voltage waveform to ensure it is not excessively noisy and is actually 9.something volts as your multimeter suggests, then, it they were ok I would be looking at the feedback voltage going to the opamp negative input pin 6 and comparing that to the positive input pin 5 to check opamp is working at the correct voltage level and then possibly deciding on a suitable bias resistor to drop the feedback voltage a bit to increase the opamp output.
It is not impossible that all the boards you have were from the same batch of rejected boards because an incorrect component was used during assembly, the simplest solution would be to try a different seller and a different board.
