The rifle used an en bloc clip system, and it was/is a more.. finicky system than that used by other rifles of the era, which led to it jamming occasionally, under the wrong circumstances.
bolt actions...jamming? hahaha fired 2000+ rounds though my mosin and never a jam xD
Yes, I know it seems a foreign idea, but mechanical machines do, from time to time, fail to function. And I'd hardly call the Mosin-Nagant a decent weapon to compare anything to, as it's the literal bare minimum of what is necessary for a bolt action rifle to function properly.