I'll be preparing and testing an in-the-field firmware update file today. We're still unsure exactly what changed to necessitate a re-calibration of the Skywriter HAT. It may have been a hardware revision in the chip or some impossible to observe change to the geometry of the PCB. Unfortunately they still worked well enough to pass our testing process :(
With any luck, it should be possible to revive units in the field with this new firmware. Instructions will be posted here once I've done the necessary preparation and testing and sent to anyone who's on our radar as having this particular fault.
We'll be rolling out boards with the new calibration from now on, and revising our testing procedure to more thoroughly check the sensor response.