Try cleaning Cache and validating in Swarm Agent
Disable “Compress Lightmaps” in World Settings
Change in …Epic Games\UE_4.22\Engine\Config*BaseLigthmass.ini* to this:
[DevOptions.GPULightmass]
NumPrimaryGISamples=128
NumSecondaryGISamples=64
It will increase the bake time but effects will be very good.( good balance quality/time )
NOTICE: Avoid to use point lights near to very reflective (metallic) distorted surfaces (like for example GU10 bubble full-of-squares reflector type ) otherwise you will see tremendous number of strange white splotches on the walls. Probably increasing those Num parameters to insane values (i.e. 1024/512) could solve that problem but the bake time will be too…ooo long an results can be uncertain.
Probably you made this problem by using very complex object with huge number of UVW islands and overscaled LM resolution ( i.e 1024px+).
Sometimes is better to have complex object as separate sub-objects with own Ligthmaps and simpler UVW and then put them together into an single Actor Object.As I noticed the SWARM uses single CPU thread for certain lightmap. So even if you have 128 CPU threads in your computer and just a single one very complex LM then only single one CPU thread will be used for calculating that complex LM ( !!! insane waste of CPU power 
)
Very long CPU afterprocessing can be visible also when you are using very dense VLM cells ( very small size like 1cm ).
Thank you very much! Yeah, indeed I have a bunch of complex meshes merge in to one SM. I finally did it, but my fix its leaving it baking and let it be like half an hour more, even it looks stuck and not doing nothing. Was more like that I got scared because didnt happen before.
Thank you anyway for taking your time and replying me, means a lot. I’m currently finishing my demoreel, that I would post it in here so you will see how I lighted my scene.
GPU baking it’s amazing.
Hello
First I’d like to say “VOTE FOR PRESIDENT!”
No really man everyone already benefit from your hard work. Thank you.
I need to ask something about HDRI.
I’ve loaded an HDRI map, made all the necessary configurations but it looks like there’s no light coming in.
I read almost all the posts in this topic (many of them say that HDRI works without any other source of light) and I can’t seem to make it work.
Please have a look at the attached screenshot
Unreal version: 4.20.3
using
GPULightmassIntegration-4.20.2-UnifiedSettings
If anyone knows and like to reply back, please.
Thanks again
HDRIs are not a replacement for having a directional light for the sun. It’s just how the engine is designed.
I see. But it looks like this fellow made it without any other light source. He’s using HDRI, deleted all the rest of the light sources and a nice light comes in from it. He’s even using Luishuangs’ GPU lightmass:
watch?v=yFtxB5u6u5I
That dude just increased Light Map resolution to 1024 for his walls to have less blured shadow ( more pixels take shadow casting information so the shadow edge will be more defined)
If you want to have very defined shadows using HDRI you could try also tweak HDRI texture parameters such as Brightness Curve (for contrast) + Brigthness (for lightness).
Light Map res at 1024 = already did that.
HDRI
i. brightness curve set to 0.5
ii. brightness contrast set to 0.5
I also set the above to 2, still no luck
I’ve uploaded the above project if anyone wants to have a closer look at it:
The SkyLIght HDRI is something different that Sphere that you are using for background.
Skylight is the real emitter but that Shpere is only a background texture put on the huge sphere object to mimic the world.
Remember that you have to rotate Skylight HDRI via its special rotation parameter called Source Cubemap Angle ( and rotation direction is opposite to the rotation of all objects in scene - surprise ?!!! 
).
If you want to have Sun “visible” via your room hole you need to rotate SkyLight HDRI by using that parameter.
So if you for example see the Sun on background Sphere map via your hole then try to rewrite Z rotation value form that Sphere to the Source Cubemap Angle with MINUS.
Then you should see the shadow after bake.
Unreal is not so easy and full of nasty surprises created in dark developers minds 
Good luck!
Thank you man, but I’ve literry done all the above (they are saved on the project file if you wanna have a look).
I did set the rotation of the “SkyLight HDRI” same with the HDRI rotation.
Still, no “sun” light from the HDRI.
How did that guy do it? How do we get HDRI light in? He’s using Luoshuangs’ scene and his GPU lightmass!
Here you go dude. The secret is to go into your texture settings (just double click on it in the content browser) and then change the mip gen settings to ‘NoMipmaps’. That will prevent Unreal from compressing the texture and it use the full light range in the image (which will give you the sun accuracy you’re looking for).
I did this quick render using GPU lightmass - but remember that GPULM will convert skylights to ‘static’ if you try and use them as ‘stationary’, but I don’t think you need to worry about that if you’re doing a single lighting condition.
What kind of sorcery is this?! Look (the attached image is after production render - I’ve set the thingy to NoMipmaps
Is it because of Unreals’ version? I’m also using Luos’ GPU Lightmass
I suspect you didn’t hit save in the top left of you texture editor window before baking.
I’m using UE 4.22.3 , but I doubt the version should make a difference here. I’ve been baking sunlight from HDRIs for a while on older versions than 4.20.x
I baked that image using Luos’ GPULM too, no difference there.
The only other thing I may have done is set the ‘EditorSkySphere’ you made to ‘Movable’ so it’s not included in the light bake. It should have no contribution to static lighting and should only serve as a realtime background.
Yeah I did save it after I put it on NoMipmaps.
Just tried setting the EditorSkySphere to Movable, no change…!
Ha, actually, I was wrong. I just redownloaded your project file and ran a light bake without making any changes and it worked - including the sun light.
You should update to the latest version of UE, there may be a bug with the version you have.
You should definitely use the ‘NoMipmaps’ trick in the future though - you probably noticed that your backdrop got A LOT sharper. UE just won’t render 4k textures at full rez otherwise.
Another tip would be to use this cubemap projection method (below) on your ‘EditorSkySphere’. It will mimic your skylight projection accurately (infinitely distant). The one in the original video you referenced fails because it remains fixed to the inside of the sphere it’s on, so it falls out of alignment with the light bake.
let me know if you’re still stuck.
Good morning man.
I just tried it with the latest version of UE4 and Luoshs’ GPULM but still no luck.
Can you please upload your modified to have a close look?!
Not sure is this GPU ligthmass affected but I noticed that original lightmass encodes light color info with wrong exponent.(2.2 instead of 2.0)
This affect brightness and color saturation quite much.