Bad lightmaps after setting Max Size to 512

I was optimizing the build size by using 512 instead of 1024 in Max Size for the LightmapColor and LightmapScale files and after the build I’m seeing these white lines in the wall edges. I tried setting them back to 1024 and it’s OK, then tried combinations and the problem are the LightmapColor files with 512 in Max Size, any clues why is this happening?

Lightmap resolution is based on how much detail can be processed into a Lightmap texture. The higher the resolution is, the more detail you will get. For your case, 512 is simply not enough to get enough data into the lightmap and introduce artifacts like that.

Also, try to increase texels per world unit, under Bake->Resolution. That might help, but not guaranteed.

This looks like light bleeding to me. Are your lightmaps UV islands perhaps too close to each other?