Although there haven't been a huge number of reports of file damage yet, the situation appears serious enough to warrant its own fresh warning thread.
The file deletion problem (which is quite real and fairly widespread) occurs if you relocated any of the special User-Profile folders (e.g. the "Documents" folder) to some other place using the tools Windows provides to do so.
If you used the Windows folder relocation tool, but there were still files in the original default folder location (this would usually be the case), those files are the ones that get deleted.
This is a major screwup, because:
And this one you'll have to copy/paste/go because we can't link to it:
https://arstechnica.com/gadgets/2018/10/microsoft-suspends-distribution-of-latest-windows-10-update-over-data-loss-bug/