For settings, how many lights are in your scene, what are their settings, do you have a skylight, what are your project settings for lighting, etc.
I’m not an expert, but it’s usually best to start with the basics:
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Lumen uses mesh distance fields which are generated based on import scale, which in turn is based on the real world scale of the object. So if your objects were very small to begin with and you scaled them up, you would need to adjust the mesh distance field resolution to match the new scale. You can check if this is the problem by using the mesh distance field visualizer under Show->Visualize->Mesh Distance Fields
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Lumen itself uses real world scale to calculate its distances. The documentation gives an exact thickness that all walls should be to prevent light from leaking through. If your scene is too large or too small in real world scale, this can cause problems.
If it’s neither of these things, this video covers some additional problems: Unreal Engine 5: How To Fix Lumen Shadow Maps (UE5 early access) - YouTube
I don’t know that that’s what’s going on, but it’s a good idea to check these first.