Rendering URP reads file after game load, due to prefab?

I have a scene where the level is loaded from a txt file.
So the monsters are loaded using Resources.Load from a prefab under resources.
This is done so not all the monsters will load into memory, even if they are not used in the map.
However, I load the prefab on the first frame of the scene, yet there seems to be a Read from a file in a specific place, apparently when the monster is not culled anymore.

When does the assets of a prefab loaded with Resrouces.Load happen? And how I make sure all Reads from files happen in the first frame of the scene?