Seems strange then if you have similar setups working fine in other places. Personally, I usually have the goods producing factories connected to like four cities, which usually gets them up to 400 quite quickly. I’ve actually never done it the way you do it, leaving the goods untouched.. there’s money to make 🙂
Anyway, I’m out of ideas. Good luck to you! And please do tell if you find the culprit! 🙂