AI units tend to have quite a few issues navigating around Agia Marina. They often get hung up at or even inside certain buildings.
In particular, the AI seems to have trouble crossing the two bridges: they often get stuck on the bridge and end up circling within a small radius on the bridge. As far as I know, once they get stuck on the bridge, they cannot get unstuck through normal means, including giving orders or assigning a new waypoint. They tend to get stuck closer to the middle of the bridge than on either side where it joins the terrain.
This can happen with single AI, but is more prone to happen with groups, due to added difficulties navigating with groups. {F20702}