If "The Tower on the Hill" is still active in your questlog (uncompleted), the script breaks if you hand in "Scarred Wood" and "Unsettling Evidence". Gwilum will then not show any quest ring for the quest "Biting the Hand that Feeds", which opens up the quests in the Northern camp. Thus you get stuck at having done 25/26 of the Carreglyn quest deed.
I found this out because I was doing the same quests together with my boyfriend, with the only difference that he did have "The Tower on the Hill" completed. He got the followup quest, I did not.
It might of course also not specifically be "The Tower on the Hill"; perhaps you are not allowed to have any of the previous quests active in your quest log. Has anyone else encountered the same?
I've both sent tickets and reported this as a bug in-game. GM responses vary between "Please report this as a bug" to "We cannot give game-specific details of this nature. Try the Advice channel." There doesn't seem to be a solution for this so far.