After sleeping in survival mode, some areas become dark, as if the light level is not computed. This only effects small areas, wich have blocks directly above them. Placing a light source in the affected area results only in that light source affecting the light level. Only after the new light source is broken by hand, does the immediate area around it update its light levels and display light from light sources, which where there before the bug occurred.
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We're tracking this issue in MCPE-85614, so this ticket is being resolved and linked as a duplicate.
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