Thanks!
Yep, there's supposed to be a piece of metal there that keeps the cylinder from sliding off the crane. Not really dangerous, but I can see how it could get irritating when you swing out the cylinder. I don't think they sell that without the entire sideplate, but you can always e-mail genny@cz-usa.com at the factory and ask if it's a small part they sell separately.
That's a Model 15 you have, by the way.