Yes I did open the right chest ,it was my first kill this week, I messaged the support already and they confirmed me it was a bug , they told me to report it here.
Hello ,I'm currently doing the envoy armor collection and I encountered a bug on Kill Construct.I killed the boss with Itzel Poison active and I didnt get the spiritual strings from the chest as it's supposed to.Here's a screenshot of me in front of Kill Construct's looted chest with Itzel poison still active.This was my first kill of the week if you are wondering.https://imgur.com/a/4d4zsRX