Sabine's injury, like Dake said, the sword fight in the last episode of Ashoka, even some scenes in The Force Awakens (off the top of my head.)
I don't know how to pull it all together in my head at the moment - I remember Obi-Wan getting cut in half and disappearing, but in later stories we have people like Sabine who survived and guys like Finn getting in duels where the lightsaber was blocked by someone else's weapon.
Cortosis, or something like it, and possibly the wider use of beskar does make sense, though.
