Cause: The hotfix resets user preferences.
Solution: Copy your saved allegro.ini from before the update back to %HOME%\pcbenv.
This is the hardest part. Cadence has removed SPB 16.5 hotfixes from their official download portal (Cadence Downloads) because the product reached End of Life (EOL) in 2016.
PSpice / Simulation
PCB Editor / Layout (Allegro)
Schematic Editor / Capture
Libraries and Package Editor
User interface and productivity
CAM and Manufacturing outputs
Product Family: Cadence OrCAD / Allegro SPB (Silicon Package Board)
Base Release: 16.5
Report Focus: Hotfixes (HF) and Updates (e.g., v016, v017, v018, v019, v020, v021, v022, v023, v024, v025, v026, v027, v028, v029, v030, v031, v032, v033, v034)
Release Period: 2011–2013 (Extended Support) OrCAD 16.5 Hotfix SPB 16.5 Updates