Those two lightmaps...they look the same right?...but are they the exact same pixel size...the exact same color depth...even if they are, how much video memory is left after loading in the mesh, the textures, the original lightmap, and the lightmap you want to swap it with and anything else that's loaded in video memory when the problem occurs...
Try this...load in the level...swap the lightmaps so the problem occurs (use entitytexture)...then swap back to the original lightmap(again useing entitytexture)...if doing this restores the original lighting then the problem is most likely related to the second lightmap...either it's not the same pixel size, or Blitz has had to do something funky to match up color depths (or even reduce the texture size so it can fit into videomemory)...but if you can't get back to the original lightmap after swapping them then possably the UVs are getting messed up...
Try this...load in the level...swap the lightmaps so the problem occurs (use entitytexture)...then swap back to the original lightmap(again useing entitytexture)...if doing this restores the original lighting then the problem is most likely related to the second lightmap...either it's not the same pixel size, or Blitz has had to do something funky to match up color depths (or even reduce the texture size so it can fit into videomemory)...but if you can't get back to the original lightmap after swapping them then possably the UVs are getting messed up...