Apparently this is a not used image from the last event. Richelieu and company find a Siren facility inside the Mirror Sea, where there are many "mass production ships". Apparently, according to Le Gallissione META, the Sirens were experimenting with the concept of the 4 Horsemen of the Apocalypse and used those robotic replicas as a test.
It was used. During the time Argus is explaining what happened to them to Implacable. In the Memories it's the #9 event.