Minecraft – How to disable command block logging into the log files in minecraft

You can set the Minecraft Directory in the Profile Editor.

Go to "Edit Profile", and check "Game Directory" for each profile. The game will create new folders for saves, resourcepacks and logs. It will continue to use the appropriate version you selected for the profile (found in the "versions" folder), rather than download the game files again.

You can then move the saves you have to the save folders for the correct profile.

Each player has their own file in a world's playerdata folder, named by their UUIDs:

These files contain their inventory, location, health, etc.

Note: If it's an older world there may also be a players folder with similar files. Ignore this, it is obsolete and does nothing.

In addition to this storage location, on singleplayer, the player's data is stored in level.dat, always under the name "Player". This file contains other data, and you need to use the editor NBTExplorer in order to view contents and manage the data:

On singleplayer this default "Player" version takes precedence. If it exists, it will always be used first, and it doesn't care who the user is, so long as it's singleplayer. Both of these locations are saved to with your current in-game data.

This means that you can play a world on singleplayer with one account, then give it to a friend (or upload it to a site) for other people to continue where you left off (still on singleplayer), it will use the Player file rather than the one specific to your UUID.

As LAN worlds are created by first launching singleplayer then opening the world to LAN, this Player data in level.dat will be the data of the host, Player A. As you are now opening the world on singleplayer (before opening it to LAN), it is using the data of the Player file, or Player A's data, rather than your own UUID file.

This also means that the data for your character stored in the UUID file has probably been overwritten with Player A's data. Everyone else still has their own UUID file intact, as they've only logged into the world while it is on multiplayer.

To fix this, you'd first need a backup from before the transfer. In level.dat, delete the "Player" section and then log into the world on singleplayer. This should force it to load your UUID file and then re-create the Player section in level.dat based on that, rather than the other way around. Everything should work fine from there.