Thank you for reply.
reproduce process:
1. I use external behavior, and I complete base content and variable.
2. I add new a variable.
3. Console throw a error. I remember content is value not null.
4. behavior editor becomes empty. All node disappeared.
serialization type is binary. Sorry, I forget the error content of console, bug the bug occurred twice. And I use the Chinese language in comment. Could that be the reason?