During the saber part of the level, checkpoint triggers when in combat and can even trigger after death. This requires the player to restart the entire level if this happens.
This just happened to me during my solo legendary run…
I destroyed the 4:th corvette engine, got blown up in the process and checkpoint hit me while I was spinning out of control right before the explosion…
Looking forward to the restart 
If you die a couple of time near a checkpoint the game will load a diferent checkpoint.
I think Bungie were afraid to make a really great game and decided to add the Saber part