I invest consistently in cities, consistently at a loss. Perhaps that's because I invest at 100% production.
Very strange.
Maybe Tom has already coded in a diminishing return? Maybe frequency of investment diminishes returns?
Or maybe it's not about production, but about population? Are the cities where you invest at full population?
Is the tax rate atypical?
Is there a very large militia presence?
Has it suffered any anomalies in the past week that could cause the game to make erroneous predictions if those predictions were made on the previous week's info?
I've personally never made an investment with negative returns that I can remember.