Hi there, Thanks for reaching out about this. Just to clarify, you've been collecting Fleeting Metastasized Essentia throughout the Nether, then defeating bosses and opening the boss chests, only for the FME to not convert and be put back into your inventory? If that's the case, can you confirm you don't have a full inventory and try again? When you do, please try to capture a video of the issue occurring. Once you have one, you can upload it to a public video hosting site like YouTube, and we'll be sure to take a look.