It’s possible that the reading is just incorrect if the DRV8825 is still changing the voltage/current at high frequency. The best way to be sure would be to use an oscilloscope to see the current/voltage over time.
That’s based on my assumption that the driver is still pulsing at high frequency when it’s holding the motor in position because it still has to chop the input voltage(12v) so that it can maintain the current limit. I could be wrong there, it’s just a guess on my part.
Reply To: Current limit Stepper drivers drv8825