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Turn Compress lightmaps back on unless this is only for visual renders and you are not planning to make this playable.
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Set static lighting level scale back to one, that will get rid of the noisy parts at the corners.
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Turn off cast shadow on your posters, they probably are took close to the wall and won’t give you the results you want.
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I’d advise you to either use a dynamic skylight or static. Stationary hasn’t given me the best results personally.
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Do you have a lightmass importance volume? and do you have a Volumetric Lightmap Density Volume? If no make sure you have those in the scene and make sure all your assets are inside of the volume.
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Use your lightmap density viewmode to check if all assets have a similar lightmap density (this will help with determining the appropriate lightmap size per object.
Hope some of these help.