If you tried to find the Z-probe offset of the Z-probe with mesh bed leveling compensation enabled, the Duet board will add the heightmap compensation on top of what you think is 0. So, when the bed is touching the nozzle in one of the steps above, and the Machine Status tab displays a value of -9.4. Due to a local heightmap compensation value, the actual value might be -9.2. But you would have no way of knowing this. Therefore, it is important to disable the bed leveling compensation. RepRap firmware already has a few safeguards in place to prevent conflicts such as these when running G29 multiple times in succession, but these are known to have bus. We recommend running G29 S2 before doing any of the actions in the list above. If you forget to disable mesh bed leveling, you will not have catastrophic results, just an error of around 0.5mm or so. Just barely enough to mess up your print.