hydraulic operated slides in an rv use hydraulic pressure to open AND to close the slides.
Fluid is ported from one side of hydraulic piston to other side
This is done via solenoid valves at the hydraulic reservoir.
When opening/open pressure is held on piston by solenoid valve
When closing/closed pressure is held on piston by solenoid valve
If pressure bleeds off nothing to hold slide out in open/closed positions.
Solenoid leaking thru allowing fluid pressure to bleed off
Slide out bars are OK.........bright red ribbon from them/place post-it note over control switch----something to remind you so that damage isn't done by trying to open with bars in place