NetworkServer method to spawn map objects (once in a match)

Hello!

Could you help with the queston - which method to use if I want to spawn any map objects once after level was loaded? Let's say we create moba game and what is the right way to spawn such objects as towers, cores etc. Obviously it needs to be spawned once before any player is connected.

I can not find any method ("signal") of NetworkServer that is called once a level is ready to connect players. I tried to use OnLevelWasLoaded but sometimes it produces errors like: NetworkServer is not active yet.

So, where to spawn map objects that should be spawn once in a session? Thanks.