Sorry, bro, don't know what to tell you. I could give you my save file but I'm not sure how it would help if it's the code that's wrong.
I don't mind cooperating. Feel free to copy paste my code if you want. Although, godot's mod engine is kinda poopy, and a few people have doubts of getting a true mod ecosystem off the ground (see Kyler2's comment here https://itch.io/t/317223/pony-race-mod-wip-testers-needed). The <addto> command theoretically would enable mods to place nice together, but it isn't able to make every change needed when modding. Simply overwriting the whole function or var or whatever is too convenient most of the time when modding. For those reasons I don't think I would be willing to put time into making out mods compatible (until godot's mod system gets revamped).