Currently having a bit of a problem with pier's

Mods used. COS, most of x deconstruct, bridge mod, D&W and necro revamp.

When I first start a game and found a city next to a river, I have the option of building a pier. Because my build order has merchant and monument first that's what I did. However, after building these, the option of building a pier no longer appears in my build list. Likewise, and new city build near a river, also has no pier in its build list (after my initial city has the problem). The bridge building is unaffected, and both my first, and subsequent cities (as long a built on, or snaked to a river of course) can build one, showing that the requirement for pier building are indeed meet, map wise at least. Also, if I start a new game, again the pier IS in the build list initially.

Is there a mod conflit, or have I missed something?

Cheers