The deflecting the washers seems odd. If you have set the z offset and used the other M code command to save it to the firmware then that setting should stay with your printer even if you switch to another computer.
Have you double checked to see if your x-axis is perfectly level? On one print i had my machine mysteriously only turned one z-axis screw for a few seconds and it totally screwed up my x-axis level. So i had to manually turn one of my screws (while the machine was off) to relevel my x-axis.