While playing with Space Exploration, any time a player that died while controlling an avatar was forced to respawn, they lost their old character. If you haven't figured out by now, the old character (and their inventory) is still in the control center. You can go up and destroy the control center and access their inventory like a chest. What you do to the old character after that is up to you.
I don't have a nice way to clean up these old characters without possibly causing issues with other mods.
This "fix" will still go through the normal Space Exploration respawn, however no matter what you select, you will be shunted back to your old character in the control center. I cannot block the respawn from Space Exploration at this time, so I need to work around it.