What keeps on happening to me: Upon starting Ubisoft Connect, it will download a 500MB-ish patch which actually downgrades me to version 11.x
This will cause the DLC to be unavailable, alongside my savegames which rely on it.

Restarting Ubisoft connect a few times (so far) has triggered the re-download of the actual new patch (2GB-ish), which will make the game playable again - until the 500MB patch strikes back...
So, i will now disable auto-updates and hope this helps for now.

Anyway, maybe this is similar to some of you, good luck.

What keeps on happening to me: Upon starting Ubisoft Connect, it will download a 500MB-ish patch which actually downgrades me to version 11.x
This will cause the DLC to be unavailable, alongside my savegames which rely on it.

Restarting Ubisoft connect a few times (so far) has triggered the re-download of the actual new patch (2GB-ish), which will make the game playable again - until the 500MB patch strikes back...
So, i will now disable auto-updates and hope this helps for now.

Anyway, maybe this is similar to some of you, good luck.

Restarting Ubisoft Connect several time eventually prompted the original Update to be downloaded again - which also restored access to the DLC (and old savegames) for me.

@fabian-0801
Same problem here!
I assume the game automatically loads your latest pre-DLC savegame, since the ones based on High Life can no longer be loaded.
I copied my savegames (they should still be around!) in case cloud-sync screws things up even more...
Go to <your documents folder>\Anno 1800\accounts\<account id number>\<your name> to make a backup of your save file.

And then we have to wait for a fix to restore the DLC....

@ubisoft Any info on this issue?

Edit: Apparently, if your game version is 11.x (bottom right in main screen), that's not correct (should be 12.x) and restarting ubisoft connect should (hopefully) download the right patch.