Save files all gone - Xbox Series X

I can no longer save at all under my own account. Every time I've played for the last few days, even when there sometimes doesn't appear to be a problem, saves disappear, whether new or my old saves. 

I believed this issue was due to the number of photos in my Sim's personal inventory, as my favourite career is Interior Designer, and my sims always end up with hundreds of before & after photos in their inventory, but even deleting the photos after every job this has happened. 

I do think it may be connected to this pack though, as the first clue I have that something is wrong each time has been that the before and after photos have disappeared at the "select photos for the reveal" screen, replaced by the grey winged lama thing. After that the Error Code: 0. comes up when trying to save and the whole save is gone forever if I log out.

I've researched as much advice on this as possible and tried everything I could, but none of the following has worked: 

• Having fewer save files - I only had 2 in the first place, now I have none.
• Reducing the amount saved in my gallery - there is now a fraction of the number of lots/sims etc in my saved gallery than there was for the past 8 years of playing
• Reducing the number of items in my Sim's/lot inventory - this has happened even when only playing for an hour or so, and the Sim barely has anything on the lot or in inventory
• Hard re-set of my xbox: I followed very specific guidelines on rebooting xbox, it seemed to work for about an hour (a save file was at least generated), but then it disappeared
• Removing my Microsoft account from the xbox and re-adding
• Checking xbox storage space - I have 60% storage space free on the xbox (Series X)
• Logged in under my husband's Microsoft account on the same xbox. Played a save from 2018 that was fine and did not have this issue at all

• Connection - I have a strong, 300mbps connection that I haven't seen drop out at all

I have all the packs and add-ons, when something similar to this happened a few months ago, I was told to uninstall and re-install everything. It didn't help that time and as there are so many, I would really rather not do that again. 

I really want to know why this is happening. It is so disheartening.