Yes, there some restrictions for using SFD (Vehicle Diagnostic Protection).
Request limits:
Up to 100 requests per user per hour
Up to 40 different VINs per user per day
Up to 1000 requests per user per day
You'll get a notification if you reach any of these limits. You might need to wait about an hour to continue accessing SFD-locked control units.
Note: The SFD unlock feature won't work if you're located in China.