Problem creating a database

Hi all,

I'm hoping someone can point me in the right direction. I've got a PostgreSQL 10 server instance on CentOS 6, which I set up and manage. I have full admin rights on this machine, so I can access logs, etc.

Recently I attempted to create a new database in this cluster. The command succeeds, but when I try to connect to the new database, I get a "could not open file" error:

It has been some time since I set up the database, so I don't know how long ago this became an issue. I can't seem to find any other instances of this problem online either. The logs are not helpful - even on the highest debug setting, I only see the "connection authorized" then the fatal "could not open file" error.

The data directory is on a separate disk array to the OS. Recently checked it and there are no disk errors.

Any thoughts or ideas would be much appreciated.