Could someone explain me why there’s those weird green/red/blue artifacts on the lightmap, please?
It’s not an auto-generated lightmap and there’s no overlapping UV’s… I tried to double the shell padding on the 3D software, doesn’t change a thing, so probably not that?
also scaled the lightmap in unity but the “colors” are still there
Block compression formats can often cause discoloration artifacts like this. They’ll be especially noticeable with white uniform albedo.
Try disabling Lightmap Compression entirely in Window > Rendering > Lighting > Lightmap Compression, and then re-baking the scene.
Another thing to try if that doesn’t work is to set Lightmap Encoding Quality to High Quality in Project Settings > Player > Other Settings > Lightmap Encoding.
Let me know if either of those make a difference 
Thank you very much for your answer!
The Lightmap Encoding Quality is already in High Quality but turning off the lightmap compression did work!
Just a quick question tough: will it become a problem in term of performance after I’ll add all my props? It’s not a big scene tough: One room, a few modular assets, some midpoly and around 20-25 props.
You are asking whether turning lightmap compression off will be an issue? It depends on how many lightmaps you have, which size they are, and which devices you are trying to target. For smaller scenes it’ll usually be fine.
The primary downside to turning off compression is that the textures will use up more VRAM. Take for example BC6H, one of the most common block compression formats. It uses 1 byte per pixel. If you use no compression, which results in a full HDR FP16 format, that same texture will use 8 bytes per pixel. That’s an 8x increase in VRAM usage and memory bandwidth.
Now, if you just have a few small lightmaps, this may not be an issue. For a 256x256 lightmap, this size difference would be ~0.5mb vs ~0.07mb. Both of these sizes are very small and the difference is negligible. If your lightmaps are larger, it’s going to matter a lot more. For a 4k lightmap that’s 128mb vs 16mb.
If you are interested in still using compression, some other ways to work around artifacts are to hide them with clutter or fiddle with scale in lightmap settings a bit to hopefully move the artifacts or eliminate them. Also, check which format is actually being used - some look much better than others, you control which you get using the Lightmap Compression dropdown.
I’ll check that, thank you very much for your help!
This has always been a go-to resource of mine when troubleshooting baked lighting issues. Hope this helps.
Yup, it’s an amazing documentation there, already read it a few time 
Unfortunatly, I’m still struggling with the seams of my modular set (wall, floor and all) but that’s an other topic ahaha
