I went through a stretch with Zoey like this. I thought injury at first, but she checked out fine. I stopped using the harness and switched to a flat collar, that helped but occasionally she would still stop. I would disconnect her and just walk for a bit, then hook her back up and go again. She got over what ever the issue was and is fine now, she runs like a maniac most of the time, glad I have hydraulic disks. Zeeva may pull out of a flat collar, but maybe check the fit of her harness and see if its irritating her.