To recreate issue:
- open project
- open Sub.gd in the script editor
- make some small change (ex comment/uncomment i.init() ) DO NOT SAVE YET
- Quickly save the file and exit immediately after
- Re-open project. Repeat if necessary
To fix issue:
- open project
- open Main.gd and comment the line "var sub := preload("res://Sub.tscn")"
- save project
- exit editor and reload
- uncomment the line