What I did: I resized the sidebar so it takes up less width horizontally.
What happened: It keeps my layout setting until I quit and re-open the app. The window is back to a layout I didn’t want (sidebar too wide).
What I expected: for it to remember my layout.
Things that might be helpful to know (Agenda version, OS and model, etc): 6.0.1, macOS 10.14.6, iMac 5K (2017).