There are several circumstances where your application may be considered a non-routine application. They include:
If you request to change your personal information such as your name, sex or gender identifier or date of birth
If you missed a test, interview, or hearing
If you are requested to submit additional documents such as fingerprints or residence documents
If you are requested to attend another interview or a hearing after attending an interview
If you failed a test
If you failed to meet the language requirements during your interview
Note that if your application is non-routine this may result in substantial delays in processing.