According to the documentation and in the samples, to prevent multiple spawn when spawn prediction is used before spawning the following should be checked:
SystemAPI.GetSingleton<NetworkTime>().IsFirstTimeFullyPredictingTick
But even while checking, if it is the first fully predicted tick, I spawn multiple entities.
The spawning logic happens in the PredictedSimulationSystemGroup.
Is there anything else needed to prevent the client to spawn multiple entities for only one spawn event?
The server works as expected and only spawns one entity.