you will want your uv shells to have some space (padding) in between them. It looks like your top/bottom/sides are attached or right next to the walls. If the walls are being lit and the top/bottom/sides are in shadow then you will have light/shadow bleed. That’s why you want them separated and with padding in your uvs. you can do this in your 3d package or in unreal as long as the uv shells are split already.
In the static mesh editor expand the build settings. check on generate lightmap uvs then hit apply. also the min light map setting will adjust the padding. lower values like 64 will give you more padding. higher values will give you less.
As far as skylight bounces I have never seen them set higher than 10. in the description it says the build cost is proportional to the number, so a high number like 100 would take a long time to build for not much visual impact. I would do a test at 100 and another at 10 and take screenshots to see the impact and note the times.
num indirect lighting bounce is fine to have at 100 because it doesn’t take much time to calculate after bounce 3. it also doesn’t have much visual impact either.
Good archviz settings would be something like this.
Lightmass Settings:
.1
10
10
10
.7
Good testing settings would be:
.5
10
10
4
.7
Also I would open your project in 4.19 and do a lighting test build and see if that fixes it.
let me know how it goes.