Enable Visualize > Out of Bounds Pixels under Show button in the viewport. It shows whether part of an object is outside of its bounding box, thereby not rendering fully / correctly with the lighting. It’s one of the more common causes of noise / flickering / stuttering / etc. Here’s a link to the page about it:
It may also be a resolution mismatch in the object’s static mesh editor settings for lightmap UVs. Link:
Lightmap Generation Settings#lightmapgenerationsettings
If the Min Lightmap Resolution is higher than the object’s actual lightmap resolution or Overridden lightmap resolution (in its details panel), then it can create problems.