It's making me purchase the game a second time. It is clearly in my library under games I own/ have paid for, yet it is saying I have to pay $8. Is each chapter going to be a separate purchase going forward?
No, it should just let you download it provided you had paid for the Chapter 7 release (when it stopped being free). I've not had any other reports of this and can see a whole bunch of downloads that have been successful from previous purchasers. Is it because maybe you just downloaded it for free before?