Maybe a little hard pebble got lodged in the chain and cracked the roller when wedged between chain and sprocket? Had that a couple of times on my off-road bike when riding.... engaged... over gravel surfaces.
Might want to check sprocket(s) for corresponding damage.
Agree with the previous comments - chain and sprockets should definitely be replaced!
Might want to check sprocket(s) for corresponding damage.
Agree with the previous comments - chain and sprockets should definitely be replaced!