Queue limitation

I have a queue with 4 extensions which works fine. As soon as I add a 5th extension, no one can pick up a call. Any combination of 4 queues works fine, but as soon as I add a 5th, the issue comes back. I created a second queue and it has the same issues.

Any thoughts?

Asterisk v11.13.1
FreePBX v2.11.0.34