Hi,
"Regular requirements for Student Direct Stream
International students who are applying under the Student Direct Stream (SDS) are only eligible for the expedited study-permit program if they can submit a full application. Otherwise, they have to apply under the regular process or wait until they are able to supply all the necessary documents to be eligible for the SDS. IRCC also says that there may be delays.
The SDS aims to process study permits in 20 days. Currently, international students are eligible if they are from the following seven countries: China, India, Morocco, Pakistan, Philippines, Senegal and Vietnam."
To my own understanding, if you are an SDS applicant with incomplete documents (biometrics), your application will not be processed until such time that you can provide your biometrics.