Completed bergusia forge and killed all bots for maximum temper, after i killed the boss the box came up and I opened it, but it didn't give me anything. My quest inventory wasn't full and the key wasn't at the postmaster. I also had the bug with the izanami key where it didn't show up in the lock and key quest after I consumed it.
Hi there, [quote]We are aware of new issues regarding the Mysterious Box quest for Izanagi’s Burden and are currently investigating. Players are encouraged to not use their Obsidian Crystals or Forge Keys until this issue has been resolved.[/quote] https://twitter.com/BungieHelp/status/1189680030751715328?s=20
After you try consuming it you're pretty much stuck in a state where nothing registers or is obtainable again. :/