I'm trying to find out what are the possible reasons for a cell to appear in the "Cells with Bad Land" table that is generated when you press World->World Testing->Test All Land. I am looking at some cells in a mod that look 100% ok to me, but they are appearing in the list.

The CS Help states:

Test All Land: Returns a list of exterior cells that have border seam problems.

But like I said, most of the cells in the list look fine. What else can be wrong?

I don't know if this can help, but Sometimes I've been able to see seams only looking in wireframe mode from below terrain level