Try a right click on Rocksmith in Steam, go to propeties, there to dlc and check if all the dlc's you've got are checked. If yes, uncheck all, wait for steam until it finishes loading (it syncronices Rocksmith) and then check all again, wait until the download is finished, start the game and the dlc's should be back. If not, try a right click on Rocksmith in Steam, go to propeties, then to local files and there you click verify integrity of game cache - it look for deleted files, maybe the dlc's will be downloaded then. If there are grammar or word mistakes, I'm sorry!