Are you running the proper belt? My thinking is a wide belt is pushing the sheaves too far apart. I'm no expert and not sure if this is even possible. How does it drive? Does it engage smooth when you start moving?
You’re belt is way way too low in the secondary. Bolt is loose or like said above about having the belt in the sheaves when someone installed the bolt. If that’s the case very possible your threads are damaged.
Bolt and washer keeps the clutch from outward movement. Clutch opens pushing towards the transmission as the belt travels down.
Your not on the splines correctly.
Your pushed against the spines, with the bolt tighten.
Remove secondary, check splines for damage, then put it in gear and rotate the secondary until it seat on the spines correctly.
Always lightly grease shaft & splines, only on the secondary shaft, so they don't rust together and hard to remove.