There is a known issue involving spawns that sometimes they stop working and will spawn nothing. The tech team is investigating, but at this time there is no ETA. We apologize for the inconvenience this may cause.
In the meantime, if you discover a spawn doing this the easiest thing to do is to simply look elsewhere for the monsters or if there aren't any other locations to switch gears. These issues are typically resolved temporarily by a server restart.
There is no need to submit a support ticket about this, as we are aware of the issue. Tickets will reference this Knowledge Base article and be closed.