In the city info window, it shows, among other things, how much money you are making, and also uses flashing icons to show how much this would be affected by building certain buildings, like markets or roads. However, in some cities-- and I can't find any pattern to it-- the icons flash even when I don't have anything in the building queue, and when I do add buildings to the queue, it doesn't seem to show how much those buildings will affect my income. This also makes it hard to tell how much of a profit I'll be making by upgrading trade infrastructure.
This is from my KoJ game; the buildings in the settlement don't seem to have any correlation to this, but it does seem to happen more often in coastal cities.
I do apologize if this has already been brought up.