There’s a lock symbol on our folder in susu linux

Suse Linux is the Operating System of our server.
We install our system there and make a folder named "user" where we can save our important files. But we have this common problem, this happen two to three times a week.
The user folder have a lock symbol on it and we can no longer save any file to that folder. Access denied is the message.
We then need to restart our server.
Is Suse is reliable as OS for our server?
What's wrong with our user folder?
