I have had the same problem and it's happened three times now, tends to happen after long sessions once I have multiple active regions active. Unlike this author, I am not running anno 1800 on a Mac, I'm running it on windows 11 (64-bit) have 16gn of ram and AMD Ryzen 7 4800h with Radeon graphics 2.90 GHz. The game and all DLC content purchased directly from within the Ubisoft Connect Desktop application (not 3rd party). My device should have no problem running the game yet I loose hours of gameplay when the last save and the auto saves leading up to the save are visible but not loadable.
And no... verifying files does absolutely nothing... I have tried it several times. The game has frozen several times as well.
I have played other games that are significantly more demanding with no issues, I don't have anything demanding running in the background.
I just purchased the anno 1800 deluxe dlc and it is not activated in my game, I went into the purchase history to see if there was an issue with the purchase and both Ubisoft connect and paypal said the purchase went through, I then noticed it said the game DLC that i just purchased on 06/09/2022 was "activated on Uplay on 16/04/2019". so the ubisoft dlc i just bought was activated on an account other than mine before I purchased it yet it shows up as a purchase for myself on my own account.
Can someone please help me resolve this massive blunder by ubisoft.