I think I killed all harpies including the queen when I come back in the area no more harpies spawn and I cannot complete the harpy traps quest ...

Inside the cave behind the doors at the bottom of the pit where you fight the queen no more harpies are spawning and I cannot complete the harpy traps quest

Where did you set the traps? You have to set 4 outside, and 3 in their cave. Might be the other way around...

I got the 4 outside but I already killed all harpies inside the cave and they do not spawn anymore :/

By the way I posted twice this question ... How can I delete my other post ?

If you killed them all before setting traps, I'm sorry to say, but they won't respawn and your quest will be marked as failed :( The only thing you can do is reload an earlier save.

well no worries I guess, I think they should add a respawn on harpies until the nest are destroyed ? It kind of make sense and would help people not being blocked ?

No worries :)

Yeah, that quest is all kinds of weird and it sucks that it can fail so easily. I personally thought my game bugged out when traps stopped working - it never came across my mind that I had to destroy 3 Harpies inside the cave. I was like, there are plenty outside, what's wrong? Heh. But I admit I enjoyed playing a game where not everything is spelled out for me (even with a bunch of failed quests).

I ran out of traps while outside, got the dreams, killed the queen, went back to Vergen, bought more traps from the skinny guy in the hoodie (Elgee?) went back to the dream cave and set the traps, there were more harpies when I went back and I completed the quest.

This was my experience as well. The harpies never stopped spawning, no matter which quests are complete.

More detailed:

I have played this chapter 3 times. Only one time did the Harpy Contract behave weirdly for me. In that case, after 2 nests burned indoors, I had harpies picking up traps but no quest progression (not the usual, "why won't they pick them up?"). Anyway, on the OUTSIDE portion of quarry which had already supplied the usual 4 nests, I meditated a couple of times, got them to respawn and they picked up traps, destroying nests. Weird. And all this after the Queen was dead.

In summary, this one can get weird sometimes, but I haven't had it totally break yet. I don't doubt that it breaks for some. Just don't totally write it off, though.

My mistake then, I had troubles with this quest and assumed Harpies aren't meant to spawn once you kill them. I hope BlueTrin manages to finish it :)

Thank you all for your replies, I will reload an earlier game and try to complete it !
I am a bit of a completionist and I do not know why but I feel like I have to explore every bit of the game :)

Saw from another thread that the other 3 can be trapped at the quarry area. HTH.