Was it stuck on anything or did it just never die? If its walking in a straight line, it's possible it got desynced and where the zed was seen was not actually where it was. Sometimes you can figure out where the zed is stuck, and the desync occurred, and shoot that spot to kill it. If you can get screen shots of the area in which this is experienced we can look into the environment to see if something should be tweaked to prevent it. Thanks for letting us know.