
Webster

Since we don't know the cartridge your sample example is chambered for, or the barrel length, we get to take "WAG" (Military acronym for Wild Assed Guess) at the problem.
Too short cartridges would allow "double feeding" to the carrier block but the rifle would still cycle part way.
A broken cartridge stop tab on the back of the Ladle would allow a round back into the action and preventing the Links from cycling. (Most likely suspect)
There should be a nice tasty bevel at the bottom of the back wall of the Carrier Block Mortice, to align cartridges to rise with the carrier block. A "square" profile would tend to jam.
At's about it. Basically a simple mechanism with not much to go wrong.