Didn't know whether post it in Balance or Compat thread, but here's my take. I think there should be maybe some cap for negative food production productivity, cuz with Megalopolis mod... Well, this happens XD

https://imgur.com/a/h5Bwq9J

The population went down extremely hard, although population growth is at +230k itself. So it's more of a big city issue. I did add the mod mid playthrough, so I did experience Great Starvation, but I kinda worked it out

i actually did check this, and am happy to report even at massive negative food productivity modifier the actual production is just 0 🫠. So you are not getting penalized further when you hit that. You did create a warhammer 40 k hive city though lol