This is normal behavior.
Robot mastering has a huge impact on safety, especially if it is done improperly. This is basically an acknowledgement that you have properly mastered your robot.
This also ties your safety signature in the PLC to the robot, so you can tell if something changed. It helps to make sure your safety sig means something to both your robot and your PLC.
This is the only robot I have that does this. All the others don't change SNN when it is remastered.
Thanks