Some Ender 5/5 Pro were assembled with different type of lead screw. They usually have correct firmware installed, but when a customer tries to update it, the number of Z steps will change from 800 to 400. That will cause the prints to be printed with 50% height. To fix that, ask customer to download attached Gcode file, 'print' the file and click 'Store settings' from Control menu.
Afterwards he/she should check if the changes were saved correctly under Control -> Motion -> Z steps/mm (should be 800 now).
This has to be done every time this customer updates the firmware.
If customer complains about it and ask to change the screw for the more common one, tell them the screw he has is actually better and provides twice the resolution.
This instruction can apply to various issues related to steps/mm - just change the value in gcode and you can easily change it.