Serious conversion lightmap issue from 4.19 to 4.20 (bug?)

Update:

Here is a more detailed case description.
https://answers.unrealengine.com/que…o-420-bug.html

Hello community,

since I don’t know if this is a bug, or my fault, I decided to try the forums first.

here is the thing:
I really need to use the 4.20 preview because of it’s DOF rework, it tremendously affects my stills and animations.

I was using 4.19 to build the lightmaps with the gpu lightmass made by luoshuang and downloaded 4.20. Everything looks perfect except the circular dof with it’s sharp edges.

So I loaded the project in 4.20, it complained about 2 missing plugins, since the’re not integrated yet - datasmith and substance.

But the scene opens and looks fairly good except this weird thingy

as you can see the floor panel next to the ladder has switched lightmaps with the one in fornt of the shelf. there are more objects in the scene behaving like that - but not most of them, just a few.

random objects have switched lightmaps on different material IDs, but not every object, just (imho) randomly chosen ones. as you can see, the lightmaps on the crates in the background or the pillows are correct and good looking.

is this a bug or am I doing something wrong, better to say, is there a way to fix it? I can’t bake the lightmaps in 4.20 because the gpu lightmass bakery is not available on 4.20 and i doubt it will be (soon).

thank you guys,
michael