TLDR: lost large amounts of data in iCloud storage following frozen "iCloud Settings" window on Mac Sonoma 14.0.

Setup: two MacBooks, two iPads, and one iPhone all logged in to iCloud with the same ID, and all set up to sync "desktop & documents folders". Convenient - I can review code, documents, etc. while traveling and work from either MacBook (one is large, one is travel size).

Yesterday I notice that passwords are not syncing across devices - password change on macbook was not reflected on iPhone. I go it to iCloud settings on MacBook to check if sync is turned ON. For some reason it (iCloud Passwords & Keychain > Sync this Mac) shows sync turned OFF (it was definitely ON before). I move the slider to turn the sync ON; at this point the entire settings window just freezes. First time ever I had the window completely freeze on MacBook. I wait about 5 minutes and reboot the MacBook (reboot seems to work normally). After reboot, passwords do sync up and I think "all good".

Today I realize large amounts of data is gone from all iCloud on all devices. For example, here's all that's left of a large CPP project:

project_name cpp src CMakeLists.txt tools Dockerfile.el7

That's it - two files. Out of hundreds. I check all devices, also check iCloud Drive via web browser - same. Luckily this one's also in Git. But many other documents are not. I've been completely relying on iCloud for storage of personal documents for about a year now.

Google and ChatGPT seem to not be of much help. Apple support in progress but not much so far. I would greatly appreciate any suggestions. And in general, thoughts on reliability of iCloud primary (only?) storage of important documents?