Sea trade routes not working

At least, in Capua career mission.

With an opened (paid) trade route to Syracusae, with oil set to be exported, with Docks built in the margin of the right side river (the one with birds) and 12 workers in the Docks (the animation shows docks are working)... no ships arrived at the city.

I tried twice, and both times happened the same. In the Empire map, the route wasn't drawn (the land route was).