The problem seems to only affect the Series X version of the game, with multiple players reporting the issue on the Ubisoft forums, Twitter, and in emails to IGN.I myself have experienced the issue – after playing the entirety of Legion on Xbox One without a saving issue, I switched to Series X towards its final stages. Autosave stopped working from the beginning of the final campaign mission and around an hour into the post-game. When I reloaded, my character was about to begin the final mission again, meaning about an hour and half’s progress was lost.
Without a clear cause for the issue, there’s no notable workaround, meaning playing the game on Series X currently comes with an inherent risk of losing progress. Ubisoft has now begun informing players that it’s aware of the issue, and that a fix will arrive in “early December”
We’re sorry about the issues you’re experiencing. The team is aware of this issue and are working on a fix for it, which we’re aiming to have in a patch in early December.
— Watch Dogs: Legion (@watchdogsgame) November 20, 2020
It seems the best course of action, for now, is to play the game on another format if possible – which is at least made a little easier by Ubisoft Connect’s cross-platform progression. We awarded Watch Dogs: Legion an 8/10 review, saying its “bold use of roguelike mechanics in an open-world action game pays off in interesting ways, making this visit to near-future London feel more varied than the previous two games”.