We have shipped an update to Concrete material last night.
The update was meant to switch the material to use textures that are compatible with the tile breaking method we use to reduce the amount of periodic tiling you see far away (which other materials, like cobblestone, woodplanks and brick, already use).
It appears that the texture update went a bit too far though and introduced extra dark "patches" for the texture, which unintentionally made some games that relied on concrete look worse.
We will revert the update to Concrete next week. Sorry about the confusion.
EDIT: Concrete has been reverted. Thank you for your patience.