Hey Andy,
loading is happening on the GameThread, but not fully synchronous. It’s using a time-slicing approach by default, with mixed success.
However, you can enable the ALT via the -AsyncLoadingThread parameter or by setting the following in your *Engine.ini:
[/Script/Engine.EditorStreamingSettings] s.AsyncLoadingThreadEnabled=trueBe aware that there still might be some issues with running the ALT in Editor, but we’re aiming to enable it by default soon™.
Kind Regards,
Sebastian