I always assumed that Kylo Ren's lightsaber was different from Ben Solo's because of the cracked kyber crystal. After all if it was the same lightsaber it should have the same kyber crystal which wasn't cracked. However, in Star Wars The Rise of Skywalker The Visual Dictionary it says the following confirming that apparently it is the same lightsaber:
Kylo modified his lightsaber upon falling to the dark side, channelling dangerous amounts of power through a cracked kyber crystal.
How come it uses a cracked kyber crystal and not the original? Or, if it is the original, how did it become cracked in the first place?