My brand new Ridgid router was constantly hanging up about 1/2 way through its travel up and down, no matter how loose the sleeve adjustment was. There is a small pin on the side of the router motor that registers it to the sleeve that bolts to the sled. I found that there was a “bump” in the slot on the sleeve that the pin rides in. I needed to file that bump down to correct the hang-up. If you do not have the right file, take the sleeve to the hardware and ask for a bastard file (do not ask me where that name came from). They come in various sizes, and there is one whose edge fits that slot perfectly. They cost $3 or $4, and are handy to have around in the shop. A few strokes with that file, and the bump is gone, and the Z axis works well. Also, get a short bungee to reduce the slop on the Up-Down motion, and help the router push the bit down.
On my set-up, I can put the bungee hooks on the ends of the ring and secured the bungee with a very short screw on the top of the router. Have not seen any interference with the chain rollers yet.