Fishing ship cannot be trained on Hellas (population flicker)

[AlexHerbert]

While playing on the Hellas map, I encountered a strange issue when trying to train a fishing ship.
When I clicked to produce the ship, the population number started flickering, as if I didn’t have enough houses.

However, I did have free population space, and I even built more houses to be sure. Despite that, the fishing ship was never produced.

Has anyone else experienced this?

[Gurken Khan]

Replay or it didn't happen!

jk. I venture to say it's because of the dock's position: it couldn't spawn the boat.