When Reload Scene is enabled, and you have an udonbehaviour on an editoronly object:

ClientSimRuntimeLoader.OnBeforeSceneLoad -> StartClientSim -> DestroyEditorOnly

fails to do anything because the scene has not yet been loaded, so scene.GetRootGameObjects returns nothing.

ClientSimRuntimeLoader.OnAfterSceneLoad works as expected.

The VRCSDK then continues happily

When Reload Scene is disabled, and you have an udonbehaviour on an editoronly object:

ClientSimRuntimeLoader.OnBeforeSceneLoad -> StartClientSim -> DestroyEditorOnly

works because the scene is already loaded. The EditorOnly objects are destroyed.

Then, it calls into ClientSimNetworkingUtilities.ConfigureNetworkIdsForClientSim, which tries to lookup the udonbehaviour, it doesn't exist, and an InvalidObject error fails out play mode.

DestroyEditorOnly should just be removed from StartClientSim since it never does anything in the "working" case anyways.