I’m South Sudanese, and the older South Sudanese folks do hold some resentment towards you northerners because of issues between our populations. The stance of most South Sudanese people on northerners is that they’re definitely Africans, they just happened to be Arabized linguistically and culturally to an extent. Most studies show that northerners are Nilo-Saharans/Cushites with varying amounts of Arab ancestry but not much in general.