Hello!
A few things to consider. Make sure all the fields inside the struct are market as UPROPERTY(BlueprintReadOnly) or UPROPERTY(BlueprintReadWrite).
Also, since you are using AddDefaulted, consider that all the struct instances will be constructed with their default values. You probably want to make sure that in your struct declaration, you are setting default values to each property or else they could be filled with garbage. Particularly, if any of these fields is a pointer, they will probably be null and you can get a crash if you access them.
If this doesn’t work, can you share the code where you declare your struct, and the crash stack trace?