It's a bit of an annoying message when you don't know how to fix it.
Yeah, that definitely needs more feedback in UI. What's happening is that many wonders and some other actions have either a production or gold cost. For example, Stanhencg has cost 250p. Each turn that you are building Stanhencg production is being deducted from the city but only up to 2/3 of total city production. Since it takes 25 turns to build, 10p is needed per turn. If the city can only provide 5p (50% of what is needed), then there is a 50% chance that no progress will be made that turn. So, if this situation continues, it will still be built but will take about 2x longer. Actions with a gold cost (e.g., establishing a trade route) work the same way except the gold is deducted from your total treasury (will start to shortfall only when you reach 0g).
What I can do is add feedback in the build mouseover. So when you start Stanhencg, you will see a warning based on current city production: "[red warning text]City production is too low to build Stanhencg in 25 turns; based on current production rate, there is a 50% chance for shortfall (no progress) each turn."
@400cats, the policy slowdown in v10 will hit the high-culture civs but have little effect on the low culture civs (in fact, they will get a tiny boost). So Ag civs aren't going to suffer. I described it a few posts up but probably was lost in all of my other posts:
Old math:
CL approaches 10 x
total culture generated /
total pop
New math
CL approaches 10 x (
total culture generated /
total pop)^0.7
If you are making <1c/pop, then the change is very small but actually positive. At 1c/pop you will approach 10 policies total, so 1 branch completed and a few policies into the next. At 0.5c/pop you approach 6 policies, just short of a whole branch. With 5c/pop (hopefully that's at the very high end) you approach 30 policies or about 4 branches completed. (In v9, the latter example would have got you approaching 50 policies which is clearly broken). I hate to add hard limits but I think I will add a hard stop to policy progression after 4 branches completed. If it's common to hit this, then I will bump the 0.7 exponent down to 0.6.