So basically foundations are really broke right now. Randomly it happens that they disappear, but leave a ghost. You won’t notice it’s gone before you attempt to build, when you attempt to build everything you try to place is red instead of green even when the conditions are right and then you have to waste time trying to find the broken foundation.
To fix it you have to place a new one. It is highlighted green as in the picture below if you’ve found the broken foundation.
EDIT: This also seems to happen with pillars.