Some of you have enabled the option to compute Ultra lightmaps for your maps. There's currently a bug that causes some undesirable graphics issues with maps that were computed using Ultra. After computing on Ultra the map will look good to the author, but will have graphics issues for others that play the map, since the lightmap that is embedded in the map file is compressed and not the full Ultra quality.

Therefore, we recommend that you use lightmap quality no higher than "High" until the bug is fixed.

If you've computed on Ultra, and want to see your map as others see it, just clear your cache from your launcher settings, and then open the map normally in-game via Local Play.