I have the same issue and I tried building in several different locations. I also tried building at different heights to make sure all of the foundation pieces were touching the ground. I eventually found a location where I could build enough foundation for a small house but the corner is missing out of it. It is very frustrating.
I'm glad I found others with this problem. I was going crazy trying to figure out why I can't place foundation pieces. It seems completely random where it will and will not let me place foundation pieces next to each other.