Hi cheinle,
Welcome to our forum.
In my option, this is an issues about SFB development, we suggest you post this case to SFB development forum by the following link, thanks for your understanding and support.
https://social.msdn.microsoft.com/Forums/en-US/home?category=SfB
If there are any questions or issues, please be free to let me know.
Best Regards,
Jim Xu
TechNet Community Support
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