Well to make it even easier I can share the model. No matter how your scene in unreal looks, if you get it to work it would be progress. The model is ready to be imported into Unreal with default import settings, so you can just create a new project and import.
Thank you for the help…this is really getting me down!
The model link:
https://1drv.ms/u/s!AkFvZ1Lmz5r1vj3eqBsqEqk5e2Sn?e=6Vvogt
To me it looks totally fine…
Just opened a new project, imported the mesh, gave it a 512 res lightmap, added a point light and built it production…
Ok cool. Now you will see that the cubic room is divided in two with a single wall. The issue comes in on the other side without the light when you build the lighting.
… this is not my result, even your lowest resolution build looks much, much better than mine… I will do the same, create new empty project, import model, leave all default directional lights and stuff be and get back to you… Thank you so much for your effort!
Forget preview quality!! That’s a preview!! If you want proper results go with Medium and higher!!
And don’t forget the lightmap resolution!!
Built with High Quality setting, 2048 Resolution
Unreal Engine 4.24.1
Here is the UE4 Project if that would help
https://1drv.ms/u/s!AkFvZ1Lmz5r1vj6pl3Xfj-tt4xs-?e=RmEEnQ
I’ll have some time in a few hours!
So you’re just missing a LightmassImportanceVolume covering your whole mesh/area + a PostProcessVolume to have constant exposure…
You can get away with lower lightmap resolution and a bit higher lightmass settings (ILLS 0.5 + ILQ 2 worked for me)!
Thank you so much for the help. It does not work perfectly for me yet, but I have decided to get going on my actual project and avoid this issue for now, it is holding me back too long. I have opted to use all dynamic lights in my project since it is indoors in only one small building.
Do I need to close this page somehow? Or do I just leave it be?
No worries!
You should get the same result… All I did was those changes + went lower (1024?) with the lightmap resolution + it’s a production build!!
Sure do/use what you like! 
…dynamic lights won’t produce GI…
If you feel any of the answers gave you explanation, helped to resolve your problem: you can mark it as the correct answer and mark it resolved… it can help others in the future…
Good luck!
Jeeez I thought you said you’re out of here!! :S
Ray tracing?! Really? 
I’ve never said that Unreal is for ArchViz, I’ve always said the opposite… ?!
And I’ve never said thet dynamic lights are wrong either…
GI, global illumination, is produced by dynamic lighting via ray tracing. The volumetric lightmap is another aspect that remains in dynamic lighting which uses interpolated light data from Lightmass and/or the built-in lighting system of Unreal Engine. To say dynamic lights don’t produce GI is a generalization. The skylight itself can be set to movable, and fills the whole scene with diffuse lighting, and the directional light is similar yet has more fine-tuning properties for other purposes. Unreal Engine is not merely an ArchViz engine. It’s also a game engine, and is utilized for other types of scenes that require dynamic lighting. So using dynamic lighting is not in and of itself wrong. The main concern is performance, as it’s stated to have a larger impact in memory use and processing time.
Denial can be a serious issue in some circumstances. I didn’t claim you said dynamic lights were wrong. I was being encouraging to use it and not stay restricted to baked if it’s not working. Self-accusing, I see. I meant my response as an inspiration, not to demote you or denigrate you. That was the other thread I said I was opting out of…I know, ray tracing isn’t a legit approach yet for everyone.
