Missing too much application specific information here. Has it always done this? Is having an operator cross the light curtain part the normal process? Is the light curtain tied into the robots IO/fence/safe circuit directly or is there a PLC involved. Does the robot stop immediately when the curtain is crossed? What do you then do to recover? Are you able to step through the recovery from a light curtain stop?
Yes, we (the company I work for) have multiple fixtures that use the Fanuc robot (as well as Kawasaki) and all the Fanuc robots do this for some reason. The robots arrive preprogrammed from one of our other plants. They all and always do this.
Having an operator cross the LC is not part of the process, but there are times when an operator accidentally puts an elbow across the LC or leans onto the LC causing the robot to stop.
There is a PLC involved. We mostly use the omron PLC.
Yes the robot stops immediately as do all other operations for safety.
To recover, there are times that the robot continues the cycle once the LC is cleared, other times we would have to press the reset button on the teach pendant. The Fanuc robots that continue the cycle after clearing the LC are the ones not welding the next point or two. The ones we have to manually reset to continue the cycle have no problem welding.