Hehe... I remember that part. One of my criticisms of divinity 2 is the inclusion of puzzles and curveball gameplay mechanics like this. It took me a while to figure out what I was supposed to be doing and I got lame items in the chest (tried it 3 times before moving on). It was more frusterating than fun for me. It just seemed very out of place in terms of gameplay and also location. It was like larian made a dungeon and then decided to include a super mario 64 inspired puzzle in one of the wings. I appreciate the attempt to break up the gameplay but I just felt that section was too much of a (gamism) for me to except. It just was not logical enough to make sense of for me.
Anyways, tastes aside, the puzzle is certainly do-able and not very chellenging once you get the hang of it. Jump up to the top following the platforms and avoiding the fire traps. Once the chest appears you have a limited amount of time to open it so try and jump down right in front of it. With a little practice you will have time to spare. Unfortunately, I never got decent loot from the chest.
