Assassin's Creed Black Flag Save Game

Hello, I bought Assassin's Creed Black Flag on Friday and I played it yesterday until Sequence 4... this morning when I relaunched the game, I found myself back at the beginning of Sequence 2 on the mission "We Hire." I replayed, the game saved at the end as usual, so I quit the game and relaunched it, and now it tells me to replay the mission... can you help me?

Thank you in advance.