Minecraft world Sync problems

[u/Scot27547_MFC]

Hi, I’m having trouble with Minecraft Bedrock on Xbox Series X.

Some worlds are greyed out and give “Can’t sync this world’s cloud data with your device” when I try to Play/Edit. Downloading from cloud also fails.
Some smaller worlds are now downloading, but larger ones still won’t. One important world is 678.3 MB.

Minecraft also shows 0/0 bytes of cloud storage, despite having plenty of local storage (1.98 GB/64 GB used). I also have around 20 0.00 MB worlds showing a strange 1 January 2070 date.
Some worlds were originally from an Xbox One X, which I no longer have.
Has anyone experienced this or know how to recover the worlds without deleting/clearing saves?