maxlawbr, did you solve the issue? Try pushing hard the reset button once (nothing should happen), then push the start/stop button again to stop the chrono. With the chrono now stopped, hit the reset button to reset the hands back to zero.
Some movements have the switch disengaging the chronograph cam, most probably because the operating lever pushes the chrono cam too much. By pushing hard the reset button once the issue appears, one forces the switch to engage the chrono cam again.