Can't deliver some quests

[simonozzolo]

Hi, I'm trying to accomplish "Loremaster" achievement. While doing some quests i'm experiencing the same problem: I complete the quest but I can't deliver it even if the button "complete quest" is red and clickable. Is a problem related to my character because other players completed those quests (the in-game tool proved this). So i want to know if there is a procedure to get this problem solved.

I'll link the quests that gives me this issue.
WoW Freakz link: https://www.wow-freakz.com/quest_helper.php?quest=11560&&name=oh-noes-the-tadpoles; https://www.wow-freakz.com/quest_helper.php?quest=11570&&name=escape-from-the-winterfin-caverns; https://www.wow-freakz.com/quest_helper.php?quest=11872&&name=the-nefarious-clam-master; https://www.wow-freakz.com/quest_helper.php?quest=11909&&name=defeat-the-gearmaster.

I hope to get an answer to this and not getting the ticked deleted without answer
Regards