Every so often, when starting Minecraft 1.16.1 in offline mode, the game will delete assets/indexes/1.16.json from the file structure and attempt to redownload it. Due to the game being offline, it is unable to complete this task, and is unable to run 1.16 until internet connection is reestablished. I've tried copy-pasting the .json into another directory and replacing it when it gets deleted, but no luck.