So one of the things that can interfere with ranged sneak attack is that standard Darkvision is only 12m while your ranged weapon has an 18m range. If you are in a dark area and you exceed your Darkvision range then you lose Advantage and cannot sneak attack.

Thankfully, some jerk made a build that addresses this.

https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=784086#Post784086

Blackheifer