Thanks for reporting the issue to us.
Could you please follow my steps below to help us narrow down the issue:
- Launch a new Fusion session
- Create an electronics design > create a new schematic > Reset to default layout(see pic below) > Set the panels as your preferred size and layout

- Create a new PCB > Reset to default layout > Set the panels as your preferred size and layout
- Do the same operations for electronics library design
- Close Fusion and launch it again.
Can you see the panels layout preserved?
Regards,
Sally

Sally Yang
Software QA Engineer
Fusion 360 Quality Assurance Team
Autodesk, Inc.