So not surprisingly, this discoloration issue is caused by the denoiser. You have a point light right under the lamp which creates high dynamic range on the same object:
While I do have some idea to further improve the Intel denoiser, for such cases my best suggestion would be disabling denoising all together (or use Simple Firefly Remover in 5.1) and use a higher GI samples value like 4k. GPULM in 5.1 behaves very close to the OG Luoshuang’s GPULM when IC&FBRG is enabled denoising is disabled:
And the mesh actually has a Min Lightmap Res of 256 while the lightmap res in the scene is set to 128:
After bumping lightmap res from 128 to 256 the left issues are all fixed:
Settings used:
Automatic Two Sided Lighting for Two Sided Materials
I’ve just submitted another change which should fix the black backfacing leaves. Interestingly this has been an issue since CPULM and I did a fix in Luoshuang’s GPULM but didn’t port it over. Be aware that since our surface lighting representation is inherently single sided (L1 SH but corrected to hemisphere), while it is not pitch black now there can be some directionality loss (less effective normal maps) and brightness issues, but better than before. To get ‘true correct’ results VLM (with high density) is needed which uses full sphere L2 SH, but as you guys have pointed out above, it is not really a practical advice without proper volumetric lightmap streaming support.