If you open a stasis-sealed chest before you get the armor quest that wants you to open that chest, you can't get the armor piece. For example, I opened the Braytech Exoscience chest (on my Warlock) before I got the Europa Arms quest. When I went to go get the Europa Arms quest from Variks, it did not autocomplete the Braytech Exoscience chest. I now cannot get the Cristocrene Arms for my Warlock.