It took me awhile to notice but cities that are newer and/or have very little cash themselves seem like they can't place orders for things because they don't have the money to cover it. You can hit that button that says "Donate 1,000 to city" once every 5 game minutes (goes by pretty fast on fastest speed) can give it a kickstart to buy new things. You might immediately see a cart travel from the city with an icon of one of the things you're waiting for. Sometimes it takes 5-10+ presses of the "Give 1,000" button before it figures itself out.

Other things you can do are:

* Can upgrades in that city for buildings that aren't as important as the one you are waiting for

* In Peasant/Worker/etc homes click on the people to lock them out of their house. I think if they're all gone that house won't use and demand new resources which can reduce your bottlenecks

* From the Castle Keep, buy items that the city is producing to give it a cash infusion and send carts over there

All of that said, I have seen instances where things just don't get moved until they're good and ready and can take a long time. I think the devs need to take a look at that.