[5valve]

Yes. Bearing will destroy the case if bearing cage fails due to corrosion or other factors. Balls from bearing then accumulate together untill it locks and starts rotating outer bearing race in its seat.
It could be faulty bearing if it fails after first few running hrs, or due to water or coolant constant leak if it fails in 1000-2000km range.

I would certainly rule out water in fuel or 2t oil, since not all bikes are affected.

Cracked cylinder water channel would not leak into crank during riding, but could leak down while stopped.

Casting inperfections on the cases, where water channels pass the crank area closely could also leak water inside.
Maybe not much during riding, but when cooling and not in use.
Pressure test of the cooling system should reveal a leak, but some sort of marking fluid, just like testing aircon system leak, should be used, to pinpoint location.

We're talking small amount of water at a constant rate. Not enough to disrupt compression, but enough, that slowly in 1-2 years or few months rust the bottom end, even though it is
covered in oil and somewhat protected.
I dont know how antifreeze/water mix reacts with oil covered steel, but it doesnt seem to do good.
Maybe even antifreeze type is to be consider, red, pink being more aggressive than blue.

Maybe AndreaGG from enduropuro.it has some clues, if they did any warranty replacements, like beta did.

Last picture shows old bearing prior to removal from my previous bike, how it should look like.