If you cannot find a trustworthy save file online, you can attempt to repair your own corrupted Sequence 4, Memory 1 save using the "Memory Replay" exploit.
The memory opens with a forced stealth section that has no checkpoint until reaching the prison courtyard. Players reloading a save at this exact point must replay the initial 90 seconds of climbing and eavesdropping. assassin 39-s creed unity save game sequence 4 memory 1