Hi all. The person over here - http://www.silverstripe.org/general-questions/show/9784 - was having a similar issue as me in 2009 on SS 2.3.3 - no solution was posted.
Basically, sometime in the last month, all of the images on the assets folder are lost on the filesystem for 2 sites. This includes the upload files, as well as any files created by SS (_resampled).
I have used SS on 100+ sites, including 20 others on the same server. This has happened to me on two different sites on two different servers.
On the first site, I am running 2.4.0 on a LAMP server, with DOM, userforms, google sitemaps. All rows in the File table are lost. This site has been used in production for months, without any /dev/build or flushes for that time.
On the second site, I am running 2.4.5 on a LAMP server, same modules. All rows in the File tab are NOT lost. Minor updates have been made to the code recently, but nothing involving Images or DataObjects that have images.
I have *no* idea what could have caused this. Sure, 1 server, I can see a hiccup or something - crazier things have happened. But 2 different installs on two different servers? Scary stuff here. I don't even know where to begin. I have looked through my code, I don't see anything troublesome.
Any help or direction would be greatly appreciated. The issue was here in 2009, but no solution was ever posted.