I’m a little confused by your UV screenshot. I can see that you’ve got a second UV for your lightmap (UV Channel 1) with the circled area but you’ve got the area marked “Ignore.” There shouldn’t be any overlapping UVs in your lightmap otherwise there will be some issues with your lightmap texture.
Looking at your first image, it’s also a little harder to tell if that is a smoothing group issue vs a lightmap issue. If you change the light mobility to Movable (Dynamic), is the issue still there? If not, we can start looking more at the issues with the lightmap UV. It’s also a bit hard to read the settings that are in the details panel on the right in your second image since the resolution is smaller. If you post anything with settings can you use a higher resolution image?