[ISSUE]: Light bakeing issues with modular meshes?

I’m fairly new to Unreal so I do not know if this is a common issue.
I want to begin on a modular office, but wherever there’s indirect lighting these ugly seams rear their ugly heads; see picture 1.
It’s only my modular part that this happens to. I’ve tried to search the internet for similar issues but nothing that help my specific problem.
I’ve tried to follow tutorials to see their results and what they did to get them, but they just seem to be able to plug and play.
The only models this seems to be an issue with are the ones I’ve created in 3ds max; my teacher told me it could be caused by my not models not being “Watertight” fixing that helped nothing.
I’ve tried fiddling with lightmass settings but I’m quite inexperienced so I don’t know if the problems there. All models have a lightmap resolution of 2048.
Any help is wanted and appreciated even moral support.

[Picture #1] The issue the black seams
[Picture #2] The lightmass settings
[Picture #3] The scene without my white walls, you can see there are no similar issues.

The meshes are all aligned. I’ve solved it by turning up my lightmap resolution. now my problem is that my walls are faceting in indirect lighting.
Btw my lightmass settings were wack and “random”.
As far as I can see there are no overlapping surfaces I’ve checked int the optimization visualizer and found no overlapping.

The main problem I’ve struggled with for months now is the value faceting seen in picture 2.
You can see by one of the highlights on the far wall, no faceting or seam, as soon as it’s not direct lighting, there a slight change in value / harsh line, instead of a smooth gradient.

The reason I’m doing it this way is to learn about modular environments.

Happy holidays.