Mine is a private game, but I found the cause. I got tired of concrete blocks not hardening unless I exited the game and reloaded. Happened when I had a lot of wet blocks drying. So I set the dry time to 2, very fast. I noticed that when I approach a city too fast, it shows concrete blocks in the building and such. In an unchanged game, they go away after a second. In my game, that was long enough to harden into a block that stayed. And Starvation is demanding, making longer delays in things. Long enough.