Instead of "imploding" (crashing the entire system), the Gateway should have a fallback state.
As the name suggests, literal lack of space can be the culprit. Gateways require a "sizable amount of space" to work correctly; if the spawn area is too cluttered with blocks or other entities, the wave cannot start. How to Fix Gateway Spawning Errors
The most common cause of this error is assuming that a "Game Over" or "Wave Complete" event means the playing field is actually empty.