The DEVs are also trying to make NPCs compatible with several active quests at one time. For now, I can give you a trick (might not work with all quests, but worked for me
):
now here's what you have to do in the quest (e.g.): Talk to A, he will give you A1, then bring A1 to person B, he will then ask you to talk to C who will give you object C1, give object C1 to B and will then give you the object F and the quest is done.
Now, if you have another quest involving character F, try going back one step and give object C1 to B, and if that doesn't work, go back another step (talk to C), et caetera, et caetera.
PS: I tried to make it as clear as possible, hope it is for you