I'm sure this has been said here before but as many know if you have a Treasure Breach sigil and go to a difficulty below torment (misclick, trading, playing with a friend etc) your Treasure Breach key will turn into a regular Dungeon Delve and ruin the sigil.
This has happened twice to me but I was 100% positive I had never gone to any difficulty below torment. The lowest I went was probably t3 when I was helping out a friend and I checked after I went back to t12 to see that I still had the sigil so I was baffled as to what happened to my other Treasure breach sigils that I lost some days before. The answer is echoing Hatred, when you walk in to start the encounter the difficulty modifier is set to normal. Even if you just go into the instance but never actually start the event, it instantly ruins your key. Just be aware.