So, I have Frontier at 27/29:
IDK what is missing since i've done ALL of the quests of that zone, including raid quests such as "portal", "subterranean", etc.
First i thought that it was because I had to complete Dead City and such things...but I have everything done til eclipse raid, literally every single quest...(i'm kinda a quest obsessed), and that 27/29 is really pissing me off!