What determines how long adjudication will take?

Wow - Your schedule is close to mine → I am an IC Contractor.

September 2019: Submitted Clearance
October 2019: Clearance Assigned an Investigator
October 2020: Investigation Completed
November 2020: In Pre-Adjudication Phase (to be assigned a case adjudicator)
April 2021: Still in Pre-Adjudication Phase (Per FSO, they cannot provide a timeline on when my case is assigned)