[squidsk]

There's a bug in 4.2.3 where attachments get deleted on upgrading to 4.2.3. In previous versions of vbulletin there was a bug in the daily cron cleanup script that prevented unused attachments from being deleted. That bug was fixed in 4.2.3. The problem was the refcount field in the filedata table could have incorrect values in it, specifically 0 (i.e. unused filedata) when it shouldn't, making vbulletin think an attachment isn't being used when it in fact is being used.

So when the bug preventing unused filedata from being removed was fixed it removed all unused filedata which included the filedata with bad refcounts. Short of having a backup of the attachments directory from before the upgrade there's no way to recover the lost attachments.