Where do player default skins get saved to?

We've had an issue on our server where players preffered skins that they set will randomly be reset to defaults. Just wondering A) if this is a known bug and B) where are their defualt settings saved to so that I can run an auto backup on them.

there is an auto wipe data if they dont play for a period of time, those skins are included in that, so thats probably why they get wiped

is that on by defualt bc i don't like that at all