Attached image removed from the server


My company uses frappe v12.

When we upload image attachment, sometimes this remove random image files(not the one we just uploaded) in the server. We upload image files to /home/frappe/frappe-bench/sites/[our-site]/public/files

anyone has this experience?
Is it possible, sever just remove file at some reasons?

FYI, when I do ls -l in sever
it shows
drwxrwxr-x 13 frappe frappe 2277376 Jan 20 22:35 files