Is there any chance the beta user is trying to access the file over a network file system? I know the message states it uses EXT4, but if it is a typical system, there are any number of other file systems that might be mounted. Without knowing the fstab and path to the file, EXT4 isn't a guarantee. If there is a chance of remote file system usage, that could be a problem. I don't know that it would return that exact error message, but WAL especially is intended to be used exclusively by processes on a single host due to shared memory usage.