Solo'd Encore Concerto and got all of the secrets by myself, then got to the final boss and I was teleported into the old portal room in the mission, but no portals were active and there was no way to return to the boss room. Dying respawned me in the same inactivated portal room. Adding a player restarted the mission. This wasted my entire freaking night. Screw this. LOVE NO CHECKPOINTS.