The mod Blueprint Sandboxes (3.2.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event blueprint-sandboxes::on_player_changed_surface (ID 59)
LuaEntity belongs to surface gleba (index 14) but a LuaEntity belonging to surface nauvis (index 1) was expected.
stack traceback:
[C]: in function 'set_controller'
blueprint-sandboxes/scripts/controllers.lua:201: in function 'AttachPlayerToCharacter'
blueprint-sandboxes/scripts/controllers.lua:231: in function 'RestoreLastController'
blueprint-sandboxes/scripts/sandbox.lua:411: in function 'RestorePreSandboxController'
blueprint-sandboxes/scripts/sandbox.lua:568: in function 'OnPlayerSurfaceChanged'
blueprint-sandboxes/control.lua:136: in function <blueprint-sandboxes/control.lua:134>

I have quite a lot of mods in my current mod list, but i believe train saver is the only one that interacts with the player controller.

Can I get a save-file to be able to reproduce this?

Sure. I produced a somewhat minimal save file that produces the crash. However, I still have all the mods from the previous save enabled.
https://drive.google.com/file/d/1sd0ts4KfxutVb0YTGuCnFyF8fzcN0o-H

Steps to reproduce:
- Go to another planet
- open the sandbox
- wait ~5-10 minutes until the trainsaver starts