So I'm having an issue were the extended walls are instantly collapsing with no warning.
Specifically it only seems to happen when filling terrain designations from the right side (based of the starting camera orientation for the map) when built in the ocean. Long stretches of wall (any type) pretty much always collapse, while small stretches (a few sections or less) don't always collapse.
I did test on land after it started happening and it filled with out collapsing as expected.
Really hope you can fix this as I'm using these to make a several long train based docks.