"Heimatstädte konnten nicht initialisiert werden" / "home cities could not be initialized"

Hello AOEC,
My friend recently got a problem concerning his home cities on his ESO account - they won’t open. Instead, he gets the following message: “home cities could not be initialized” (deutsch: “Heimatstädte konnten nicht initialisiert werden”). As I logged in with my account on his PC it would not work either. The version we play is “Age of Empires 3 - Complete Collection”. He has got the Steam version.
Maybe someone is aware of this very issue and may help us.