I have a PostWar 3656 Stockyard Set and the modern re-issue Horse Corral set (6-36855) and both are some of my smoothest accessories.
I have them wired to a variable voltage transformer which is crucial. Sometimes they need a little boost of voltage to keep moving or get around a corner.
Adjusting the corral for smooth operation between 11 - 15 volts seems to be the sweet spot.
I found they work best when the channels the livestock move in are absolutely clean. I have had some dust settling in over those periods when I do have time to run trains which definitely affected operation.
Lastly, you may need to put a small shim under one or more corners for best operation.
It took some tinkering but once they are working smoothly they are cool accessories.