How do I Stop this Level-Skipping Glitch??

 After completing ANY mission on disc two the game skips all missions, cutscenes, characters, etc to the Cutscene right before the last mission on Rannoch with Rann and Legion. It is unknown what happens to game choices and progress,but after the cutscene and replaces current Normandy crew with the ones unlocked up until this level, as I have yet to check. I only have one save left in the current mission, Grissom Academy. Upon completing it and its last cutscene it skips to the one I described, ONLY that one. This has never happened before, I have completed the game twice already, with all side missions and most DLC. I was confused at first so re-loaded this, numerous times with no affect. It happened on the last game with another disc two mission. Disc one missions work fine. I figured it could have been the profile, so I started a whole new profile over again and alas, it again happens. I have no idea what to do and if anyone knows or has an idea I am willing to consider it and try it. I dearly hope I don't have to buy a new disc...