The Winnebago Service Center told me that when my BR slide was creeping IN around 4" when parked with it extended that I needed new hydraulic valves, both the slide extend valve and the main retract valve.
They replaced both and from then on for several months of intermittent use, when I'd drive, that slide would creep OUT around 4". Grrr. Anyway, I contacted AZPete here on iRV2 and he mentioned that it probably had air in the system and that it would slowly work it's way out into the tank. And that's what happened. After a few (maybe 25) Extend/Retract cycles while RV camping and traveling, it now stays in when I'm driving. Leveling was/is good.
So, what you can garner from that is 1) a valve is leaking internally; 2) there's an air leak in the system so check for spots of hydraulic fluid.
According to my slide manufacturer, HWH, it's best to hold the Retract/Extend switch for 3-4 seconds each use when the slides reach their extents. I have done that for many years now.
BUT, according to AI, "The full wall slide on the 2017 Dutch Star 4369 is an
electric slide, according to RV Trader. " So I'll shut up now.