My friends PS4 world cannot load

My friends PS4 world is unable to be opened. Every time he tries to open it it takes about a minute before saying, "There was a problem loading this world," then the loading screen for loading up a world pops up and continues to load despite the previous message. Then when it finishes loading it goes back to the worlds. He knows its not a storage issue because he has plenty, but the world did recently become 1gigabyte of storage, but ever since then he hasn't been able to join. This has been a problem since early August this year & still hasn't been resolved.