Note: Please see pinned comment by Maria below for investigation results.
Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Assets/Scenes/Network Game Scene” Scene
3. In the Hierarchy window, select “Character-Template” (Game Scene Content > Character-Template)
4. In the Inspector window, observe the “Add Character To Initiative Tracker“ and “Give Control To Selected Player Controller“ buttons
5. In the Project window, delete the “Assets/Scripts/Editor/MeshSymmetry2Editor“ script
6. Repeat steps 3 and 4
Expected result: Both buttons are still visible
Actual result: The buttons disappeared
Reproducible with: 2022.3.0f1, 2022.3.22f1, 2023.2.16f1, 6000.0.0b13
Not reproducible with: 2021.3.36f1, 2022.2.21f1
Reproducible on: Windows 11
Not reproducible on: No other environments tested