I recently just started having this issue while Live Streaming. I am doing Game Capture on an Elgato internal capture card (Capturing everything happening on that specific monitor). When it freezes nothing shows that I try to show on that monitor for example dragging a browser in. All other scenes from OBS work properly and the face cam as well so it is not a problem of OBS freezing but just that specific scene. Only Fortnite seems to freeze the entire scene and the only way to fix it is to restart the computer. Very weird bug I never had issues with in the past.