Robotiq Force Torque sensor value increases after stop

The program does the following:

move the robot in z- direction until it hits the obstacle ( in my case a book ) on the table

when the force in Z- direction is more than 50N a textmsg is logged and the movement stopped

The strange thing is that the force from the Robotiq sensor is still increasing, how could that be explained? Looking forward to your ideas.

Attached I send the shortened and marked logfile of the robot, it is still a bit confusing but the important lines are marked with some asteriks *

Log_Contact.zip (10.5 KB)