The mod trainsaver (0.0.24) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event trainsaver::on_train_changed_state (ID 25)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__trainsaver/control.lua:193: in function 'target_is_locomotive'
trainsaver/control.lua:781: in function 'update_wait_at_station'
trainsaver/control.lua:1115: in function <trainsaver/control.lua:1112>

This occurred as a took a screenshot for another issue lol

Thank you for the report. This was a strange one but should be fixed in today's release, version 0.0.25. Please let me know if you encounter any other issues!