p.Chaos.EnableAsyncInitBody is read-only and needs to be changed in your DefaultEngine.ini.
You can check if it’s enabled or not by opening the console and entering p.Chaos.EnableAsyncInitBody without any value, and it’ll say the current value and where it was last set. The console should also warn you that it’s read-only and can’t be set that way.
If you’ve tried setting it via ini changes, you may have modified the wrong file or done so incorrectly, what changes did you make and to what file?