been dealing with lifttrucks for over 30yrs
never have seen any widespread issues with liftchains breaking except only in an operator abuse situation
specifically in your case with the paperroll clamp on that big truck?
the truck being a 100 series its rated at about 10,000 capacity normally, with the paperroll clamp i'm sure that was downgraded to about 8,000 or there about?
you have to take that into consideration plus how the operator is trying to handle his loads, in alot of cases when i've done work at any type of factory that handles large paperrolls they do try and pickup multiple rolls at the same time, generally 2 at a time.
how much does each roll weigh?
does it exceed the truck capacity plate rating with 2 rolls?
is the operator trying to move around more than 2 rolls by taking the weight off of several stacked rolls and sliding them across the floor?

any of these situations can be contributing to chain breakage due to overloading the chain capacity.

if these trucks are low hour(fairly new) trucks this should not be happening for no unapparent reason.

just some things to ponder to help you on your quest to find out why.

good luck!