mG are thousandths of G, local gravity. 1g = 9.8 m/s².
At some position one of the x, y or z axes has to be aligned with the local gravity, depending on the orientation of the sensor and will measure about +/- 1000 mG.
If no axis measures about 1000 mG, it is either in positions intermediate to the local vertical or it does not measure acceleration correctly.
The device may not have been configured correctly.
I’m also having trouble getting the axis values to register correctly, even when uninstalling and then reinstalling the device. Is there any way to tell the driver to reconfigure the “default” axes values without having to uninstall/reinstall?
If you mean that it does not show acceleration information on the 3 axes, it is possible that it has become blocked and you have to reset it, remove the battery and pair again.