try having a person operating the joy stick in service mode while another person slides the festoon back and forth at same time.
I've had that happen to me in the past where a wire was going bad in the festoon and it only happened intermittently.
Have 2 laserwash 4000 with docking dryer and pump stands with 3535 CAT. In operation when removed
5000 each or 7500 for both. Cheaper than buying parts if you need any.