Serious conversion issue from 4.19 to 4.20 (bug?)

I took screenshots from all the objects I could find, which are misbehaving:

247837-2018-07-19-14-13-33-window.jpg

the table is actually white.

there are lightmaps as you can see, but somehow they’re not on the right subobject. the wooden panels are not single objects, theyre merged together to a single object with different material IDs, but so are a lot of other objects, that behave well.

here are some other objects:

247840-2018-07-19-14-14-17-window.jpg

this is also annoying, the black wall should have the same concrete texture as the wall on the right, on the bump and specular map you can see, it has the same texture but the lightmap is completely black.

247861-2018-07-19-14-14-48-window.jpg