Had the same problem on White Giant, plenty of population free and production plants and think I've found the reason\a solution. There's a lot of shortages on the market for the basic items needed at the moment so think that's the problem and why it's not building since it can't get the resources needed.
Try going to the corps page, click on details next to the corp that's not building. Take a screenshot of the resources needed for the corp to be built, then go to your trade page and using the screenshot manually buy at least the amount of the missing resources directly to your country stockpile (remember to go back into trade orders after placing them and click the button next to each to change them to immediate orders instead of waiting on best price), you'll get a message pops up saying it'll cost about 1/3 more to buy them immediately but click yes, at least you'll have them.
I did that and l