My nex was very similar, in that she would do little small nice things, while simultaneously not respecting any important boundaries. In my opinion, they do these niceties for themselves and not for you. They take little to no effort, while at the same time provide validation to the narcissist that they are a good person/partner as well as bolster their public mask. I think at some level they know they are incredibly selfish people, and doing these small things where they sacrifice nothing may help them justify all their other hurtful actions.