I had a similar issues with 93 Prowler. Only one slide with 2 cylinders. The rear of the slide would come out while the front didn't.
Changes in temperature increase and decrease hydraulic pressure. These small changes push a small amount of fluid past the valve. A valve is allowing fluid to pass in one direction as pressure builds but not flow back as it cools. Enough of the heating and cooling cycles and your slide moves out.
My Prowler was out of warranty so the factory sold me a bypass kit that corrected the problem. When they designed the slide, they only put a bypass on one cylinder.
Campers with hydraulics use to come with slideout locks that were installed inside between the wall and slideout flange when the slide was in.
Thermal expansion of the hydraulic fluid will not be able to push hard enough to harm the camper if you lock them in while traveling or in storage. Don't forget to take them out when you start to put the slide out.