The below is copied verbatim from a post I read on a forum, but really nails my knowledge of an issue I’ve seen crop up in our SharePoint environment. Basically when a user checks in a document with required fields without completing those fields, SharePoint makes the document invisible to other users. No warnings, no nothing, just invisible SharePoint wierdness.
• We discovered a more troubling impact of this behavior described above in WSS, and a better-than-nothing workaround that may help in some cases where there are a lot of files that need to be checked in.
We had a Library with hundreds of files that were not even visible to anyone except the person who uploaded them, and a few files that were visible. The uploader had no clue that no one else could see them, until someone finally asked the uploader about a file they expected to see in that Library.
The invisible files were all posted via Upload Multiple Files or Explorer View drag and drop. When the uploader viewed those folders, they files appeared and were listed as checked out to the uploader. However, check-out was NOT required for that Library.
When multiple files are uploaded to a Library that has one or more Required columns, it appears that SharePoint WSS automatically checks them out to the uploader, and makes them invisible to anyone else. However, the uploader is not warned or prompted in any way to fix or check in the Library items.
There’s no problem with individually uploaded files, because in that scenario SharePoint immediately prompts for the required information.
• Temporarily change any Required columns to Not Required
• If any files are checked out to someone else, choose Document Library Settings > Manage checked out files > check the select all files box next to the column titles > click Take Ownership of Selection
• For each folder in the Library :
• Copy the checked out files to your desktop (e.g., in Explorer View), and delete them from the Library
• Re-Upload the files
• Edit in Data Sheet to quickly add the Required columns to multiple files
• Tip: If files are nested in multiple folders, create and open a flat view before switching to Data Sheet mode(Create view > Folders > Show all items without folders)
• Reset the columns to Required (or, drop the Required setting from the columns)
Hope this helps.