Honestly no idea, I'm not surprised the dialogue system is fucked in some way. Just try to make sure he doesnt walk away somehow, no clue.
"-The Deathclaw always camped to the left out of my view, so i had to get the armor and kill it in order to continue." What? Why didnt you just walk up to him?
"-After killing Kellog, i had some trouble getting the right dialogue from Nick. He always did the dialogue from when you normally come to DC after you save him."
Weird, no idea, might be console differences. Are you sure you saved him before killing kellog? And talked to him outside of vault 114?
"-The Deathclaw always camped to the left out of my view, so i had to get the armor and kill it in order to continue." What? Why didnt you just walk up to him?
"-After killing Kellog, i had some trouble getting the right dialogue from Nick. He always did the dialogue from when you normally come to DC after you save him."
Weird, no idea, might be console differences. Are you sure you saved him before killing kellog? And talked to him outside of vault 114?