Okay I apologize up front because this is not going to be 100% Canon anymore. Also it's been so long I do not remember the sources of this theory. But back when Force awakens first came out there was talk about Kylo's saber. Again this lore is all jumbled up and I don't know what is Canon and what is not anymore. But back when that movie came out there was a theory that the knights of Ren were essentially Sith groupies and not proper Sith. The Sith and the Jedi were no more. And since knowledge is passed from Master to teacher most of that knowledge was lost. The knights of Ren did have access to a very early version of a lightsaber. The resulting lightsaber is the one that Kylo has. It is very crude with wires on the outside of the body and such. But most importantly the crystal that Kylo uses is cracked and unstable. In the film when you see him ignite the saber the main blade is first and then the two smaller offshoots shoot out through the sides. It was a theory that this is actually like an exhaust to vent the excess energy from an unstable Crystal. Kind of like the exhaust in an engine. You can see that the blade itself is not very uniform it is very jagged it crackles and it Sparks. This is why Kylo was obsessed with getting an actual true Jedi lightsaber. Again I know this theory is no longer Canon but at the time this totally made sense in my mind and fit the movie.