Alright fellow pale people let's have a chat.
The reason Jake's behavior post NM is excusable is because HE is a Native POC and the stereotypes and problematic behaviors he exhibit are harmful TO HIM SPECIFICALLY as well as Native culture in general and so writing them off as the author's racist ramblings is natural. These things were written to slander Jacob and Native culture.
Jasper being a Confederate is not something we're allowed to excuse because the actions of the Confederacy and of Jasper himself are harmful to BLACK PEOPLE and not to him, his family, or any other white person. It's also written as not being a big deal.
I understand. You see a pattern, you want to know why one is wrong. I used to too! This is something I had to learn!
The great thing is: you can still like both characters. You can like Jasper! You just cannot forget, excuse, write off, or "fix" what he did. You also CANNOT speak over poc about how you feel about him.
Fix-it fic serves a purpose. You can solve the racism, the misogyny, the idiocy, and the problematic elements. But that's FIC. IN FANDOM where REAL ACTUAL FANS OF COLOR CAN SEE YOU Jasper does not get a pass. You can like him, you can make funny posts about him, but you don't get to be upset if a poc tells you they don't like him.
From one white person to another, it is OUR RESPONSIBILITY to listen to our POC counterparts on this matter and ALL matters surrounding racism.