The problem is that the user edited his post.
I have done the same thing on my forums. This is a bug that Nabble needs to address
For the moment the work-around is to upload the file again if you edit a post with a file attached.
More technical stuff follows (feel free to ignore!)...
I believe it happens because such messages include an HTML section that links to the file that was uploaded when the message was first posted, but editing is only done in plain text mode and the link gets lost during the edit process. It seems that once the link has gone Nabble then clears out orphan file that has no link to it.
What ought to happen is that Nabble should detect any message posted with HTML included and offer a WYSIWYG HTML editor for such messages.
(I accept adding such a feature might be complex to add. Most users would find working with HTML code in the current plain text editor difficult. That's why almost the only HTML messages you see on a Nabble forum are those that are posted by email.)
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.