Same problem with the hydraulic slides on our new 2017 3911FB we bought in May. Creeps out a few inches while going down the road, but especially when parked in storage overnight. We have a warranty claim in, but this process is like watching grass grow. We hope the tech can help us at the National Rally next month. In the mean time, I bought a couple of slide-out locking bars for added safety.
https://www.amazon.com/Rv-SLIDE-OUT-...s=RV+slide-out
Thanks everyone for the great info. B & B