I have seen this problem when custom objects are touching or places on top of each other. Check to see if the wind is making objects move or contact each other.
Watch to see the frame rate drop.
I have an older D_Link router and everytime i search for multiplayer games a box pops up port test failed", if i click ok on the box and search again the sessions come up." Not sure why but it works for me.
I used the Aqueduct to build on because I loved the topography in this area. It is a long course so a plane with some distance will be necessary. Enjoy