I only have experience with hydraulic slides and I have had the exact same problem in the past. First thing you will want to check are the solenoids. If they are ok then most slides have 2 or 3 cylinders that extend and retract the slide along with an equalizer cylinder. After checking everything on my it ended up being the front cylinder that extends and retracts the slides. It was a blown interior seal. These can either be rebuilt or you will need to contact HWH to get a new one. Problem with mine is they did not stock the part and one had to be built which took o bit over a week.
Jim , MJ & Spirit of Sambuca Bear
2015 Dynamax DQ320XL
Jeep Sahara Toad