Demeter miracle doesn't work as described. It's description is just inaccurate.
1. previous miracle ended. Population has fallen for ~2 hours. Screenshot made just after re-activating it. Everything looks fine so far.
2. Few hours after activation - population in cities keeps falling. However in some cities it falls faster than in others (less unhappy) cities. This suggests that the wonder is "warming up" instead of applying +12pop growth straight forwardly.
3. few hours later, population in some cities is growing steadily now, but in few it keeps falling.
Solution :
Either
- the miracle must work as it's described -> just offset population growth by +12,
or
- the miracle must be properly described -> population growth is increased via some formula. . . I don't even exactly what formula, because it's not described. And the information in city center should also be repaired, because right now city hall is stating "population growh = 3pop/h" and it is straight up not true, because population is falling.
I think first solution would be easier, but . . . . if that's not what is already implemented, that means someone changed it somehow... But the description is wrong, either way, which is bug.
I checked in Polish, English and German versions of description. No language has the effect of that miracle framed correctly, according to what it does.
(off-topic spoiler)
What annoys me is - this is supposed to be a strategy game right? Strategy games usually have clear rules, so that players can build strategies around those rules, right? So if you make a simplified description for an effect but this is NOT how that effect actually works - then you obscure actual mechanic and player that spent time strategizing just wasted his resources and time, because the description is false.