Windows 2012 folder rights

I migrated to a new server and was having issue with users being able to delete files that were moved during the migration.
I noticed that new files have a user FileVista (R0YG815V) with full permissions. I tried to apply that the folder but the user does not exist as far as I can see as a server user object. I end up giving Authenticated Users full permission and it works but I think this is a bit of a security issue to do that? Please advise

That user is an application pool identity so you need to type it like this on "Select Users or Groups" dialog:

IIS AppPool\FileVista (R0YG815V)

Then it will be recognized and added to the permissions list.