Until version 0.5.25 of Avatars there was a crash when a player controls an Avatar then their character is teleported while still controlling the Avatar. In this situation, disconnecting from the Avatar would result in an immediate game crash. This bug was reported in https://mods.factorio.com/mod/Avatars/discussion/63e072ad45729cd58c568d15 and is now fixed.

If you never saw this, then you don't need to read any further, the bug has been fixed and should not occur again.

If you did encounter the error, and you played long enough after your character was teleported that you do not have a good save to recover to, then this state can be still be fixed. If the save only had a single character with this issue, then it will be resolved immediately on updating to 0.5.25. This will require the mod to do a full scan of all surfaces, but hopefully will not take a long time. In this case, the following will be printed to the console in game:

Repaired broken 0.5.24 Avatar reference for PLAYER_NAME

If there are multiple characters with this issue, then you will see a message like below:

Avatar player references for the following players are broken and cannot be automatically repaired:
  PLAYER_NAME1
  PLAYER_NAME2
  ...
Each player must run the "/avatars_repair_player_temporary" command in the console while selecting the Avatar Control Center that contains their original character.

Steps from here to repair the save depend on the permissions of players, if all players are admins or there are no custom permissions in the game, then follow the below steps:

1. Each player should select the Avatar Control Center that has their original player character, by hovering their cursor on it.
2. They must then open the console with tilda "~"
3. Run the /avatars_repair_player_temporary command
4. If successful, they will get the same "Repaired broken 0.5.24 Avatar reference..." message from above

If they don't have permissions, or another player wants to fix the error for them, then the 2nd player can include the 1st player's name that has the issue when following the same steps and modifying the command like this: "/avatars_repair_player_temporary PLAYER_NAME1"

This command will continue to be in the mod for an un-determined amount of time, then I will remove it.