I've had the same problem on the same device (SGH-T989), using a variety of ROMs (stock, CM, AOKP, Carbon). Clean Master didn't find these files. Using ES File Explorer (root enabled) I was able to go to /data/lost+found, select all, and delete them. It was a little buggy (ES File Explorer claimed 0% completion/said there were no files to delete), but it worked.
From what I've read on the subject, lost+found are junk files and are not called by running applications.
I expect these files to reappear soon, but they're easy enough to delete.