Event doesn't start

This is being done with the default settings.
After requesting rescue, fireworks go off, but sometimes no zombies spawn and the event doesn't start.
The timer displayed at the top also remains stuck at 3m1s.

Is there a way to fix this?
If it starts the moment they spawn defendablebase, it seems to proceed without any problems.
This issue appears to occur if rescue is requested some time after a defensible has occurred.

As an aside,
If I press the down button on the elevator, an error occurs and the connection is disconnected.

Additionally, if you end the event at /warstop, only the base fence will remain.