This is one of the drawbacks of using dfao, the reason it ‘stays’ is because UE4 ‘stops’ rendering the viewport unless you have “realtime preview” enabled, depending on how you design and set up your world these artefacts will be either very noticeable or almost imperceptible but they will sadly be there because DFAO is an effect that’s applied over several frames.
The way you can fix this is to turn dfao shadow casting off on movable objects and only enable it on movable ones but this entirely depends on your use cases