If it is a livery, there’s also a potential problem where if they hard painted the registration number and having to “hide” the sim generated registration number, they had to put a empty space in the livery aircraft.cfg registration number. Back when I had this issue it wasn’t a CTD, but it was stuck in the loading screen indefinitely. Like it’s trying to render the livery with the empty registration number but it couldn’t.
So some livery creators had the idea of instead of using an empty space for the registration number. They use a different ASCII character called an transparent character. So the sim can still render that character as a valid character in the registration number, it’s just that it’s transparent so it’s not visible.
I’ve reorganised my liveries according to that now.