Same issue here, collected the treasure but didn't get credit for the quest.

There are two locations/quests right next to each other there. One is a treasure, protected by an Alp. The other is Manticore gear diagram, located inside the ruined tower (you have to climb the wall to get to it).

Originally posted by liho1eye:

There are two locations/quests right next to each other there. One is a treasure, protected by an Alp. The other is Manticore gear diagram, located inside the ruined tower (you have to climb the wall to get to it).

The one in the ruined tower is the maticore mission, which i have completed. It's the Toussaint prison experiment which is protected by an Alp that is bugged. The reason i think it's bugged is that i have collected the red treasure next to a big chest, but the mission doesn't complete

Ok, I don't know then. The treasure quest worked fine for me. There is some other small junk and corpses around the area, maybe they count towards completion....

Has anyone come across a solution to this bug?

Same here, locked both treasure, lv 47 quest still remains

Same issue happened for me, got the chest that is supposed to complete the mission but nothings happens

Well. This quest is just annoying me, since it's the only quest i am missing for 100% completion of the witcher

Same looted the chest, still have the quest. Dandelion his best to f* up this quest.

There is a tower east of the hidden treasure. Climb up and there is a loose stone in the wall. This finishes the prison experiment quest and starts the scavenger hunt for the Manticore Gear.

Edit: No, the prison experiment quest is not finished, sadly. Sorry.

Edit 2: Found it. Behind a wall east of the original hidden treasure is a chest. This one definitely concludes the Prison Experiment quest.

Originally posted by juergen:

There is a tower east of the hidden treasure. Climb up and there is a loose stone in the wall. This finishes the prison experiment quest and starts the scavenger hunt for the Manticore Gear.

Edit: No, the prison experiment quest is not finished, sadly. Sorry.

Edit 2: Found it. Behind a wall east of the original hidden treasure is a chest. This one definitely concludes the Prison Experiment quest.

Yes we know which chest finishes the quest, but having opened that chest the quest does not complete.

This ^^ Made a quick video. Sorry I have a cold and its 4am I should be sleeping.

https://youtu.be/T_e6VM6zfrw

I also had the same problem with this quest but reloaded the game before I got in that place and actually found a solution that worked for me. I believe it is important that after you defeat the alp you should not touch the glowing body or any of the chests in the area until you have collected the diagram releted with Manticore Gear quest. After you've done it, go back to the glowing body and collect the items from it starting the The Toussaint prison experiment quest. Then go to the place where the small chest is, take the note behind the stone and first use the witcher senses and look at the chest. It should glow with the red color. And only then open it. Worked for me just fine and the quest is completed. I hope it will help :)

Successful completion order datum:
- Kill Alp
- Get Prison Experiment quest
- Complete Manticore quest step
- Open Prison Experiment chest

Had bug - after looting small chest it still did not count for Q. Loading game from save and looting chest again did fix it.