Probably some lightmap optimization. It looks like the ivy doesn’t let enough light through so lightmass thinks it is 100% covering the wall there. You may have to work around that problem by painting the wall black or something similar. I have these squares behind pictures that hang on a wall for example. Areas you would normally not see.
I found a solution with this issue using Loushuang’s GPULightmass
I was currently running into this issue with versions 4.25.4 and 4.26 preview 7.
I changed all my materials with a mid grey shader, deleted my post process, deleted my reflection cube, It was a simple scene with a few walls, ground plane, handful of assets nothing big or crazy. I contained the scene with a light box and I had a small opening in the ceiling to let light in.
I have two lights both set to stationary - directional and a sky light with a sky atmosphere.
My light map density was nice and green, just 10 maps total at 2048 with compression turned off.
I played with all my lightmass settings and nothing would change the artifacting as mentioned in other posts in this thread.
using that the GPU lightmass did the trick!
with 4.26 it does look like GPU lightmass is built in now. HOWEVER, currently with preview build you need an RTX card to use it…so that is a big draw back to the current 3rd party solution.
This guy was having a similar issue he found a different solution and I just want to post it here for anyone else that is running into this.
https://forums.unrealengine.com/deve…ight-artifacts
I feel like I need to go around and offer this potential solution everywhere I see people struggling with these weird blocky lightmap artifacts.
I just solved this in our project-- it was due to invisible meshes set to cast shadows. In our case, it was new low complexity collision meshes. I thought setting them to visible=false was enough to remove them from the lighting pipeline, but you need to disable their shadow casting.
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it works for me. I did have a couple of invisible meshes and just turn off their cast shadow option. after that, the lightmap artifacts were gone.
I am using UE 4.27 and came across the same problem but I managed to fix it by remodelling the mesh and its adjacent meshes too. Did not have to use GPU lightmass or any of the the other suggested answers. Hope this helps!!!