I just started over twice before realizing what was going on; no matter how many supplies with which you end Chapter 2 and how much renown you have spent on supplies you start chapter 4 (if you don't pick up Onef) with 18 supplies which is 3 days worth. That means if you don't know this in advance (and requiring that sort of foreknowledge would be terrible design) it is VERY easy to start chapter 4 with no food and no renown with which to buy more food, making your caravan face a slow lingering death by starvation. Obviously the effects of starvation are somewhat lacking at this point but the solution is to make starvation matter.

So is it a bug that you start Chapter 4 with 18 supplies and lose any renown you spent prior to that? Because it's either a bug or an extremely dubious design decision. If it is intended to start Chapter 4 with 18 supplies you should not be able to buy food with renown prior to that point.