Viewport Options -> Realtime is the first option, when you click on the arrow in the topleft of the viewport.
I have to manually set this option each start, seems like it doesn’t get saved.
In which ini file is this setting stored?
I dont know where it gets saved, but the last time I heard about that problem, it was a bug -> which engine version do you use? reset the project and editor setting. Report it on answerhub: https://answers.unrealengine/ 