Persistent servers don't persist when no one is on them. All they do is remain selectable, but they get the same error as hosting a new experience gets when trying to start a game in them. EA was smart enough to prevent people from hogging space that was unused.
What everyone has been doing to get servers hosted is spamming the host button until a free slot opens up and they get the spot. Sometimes, you can get in in about a minute, sometimes it fails to work even after 5 minutes.
I'd like to see EA set up a queue system for server creation so you could just set it up once, and they would create it and let you play once a spot opens up. That way we could get servers up without annoying spam. Not my idea by the way, it was suggested on another thread about this issue. But it's the most reasonable fix outside of them buying/setting up more server space.