Yes, Lumen is very, ver buggy, i am doing a similar warehouse scene like the one you showed on the last video, even the lighting enters the room in a similar way, but i have the same artifacts you showed on the other Lumen video and way way more other issues, like green pixels appearing randomly, and some splotches dancing forever even when the camera is still, i´ll post a vieo and images later.
Since this is ealry access it´s important to give epic feedback, but it´s a little bit concerning how much this will improve by the time they release 5.0. In the last stream they said they priority is to make nanite draw more instances instead of adressing things like vertex painting, displacement, one sided meshes and other more important things for actual game deveopment, and with lumen who knows.