The system (via the Community user) will automatically protect questions under the following cases:
3+ answers from 3+ different low-rep users (users who wouldn't be able to answer should it have been protected) were deleted (for any reason)
Five answers from low-rep users were posted in the last 24 hours. Three answers on Software Engineering, English Language Learners, and Workplace, and 20 answers on Code Golf.
Stack Overflow only: Two answers were deleted by spam flagging.
The system will never auto unprotect a question automatically.