Steps to reproduce:
1. Create new Unity project using Universal 2D Template
2. Open Package Manager window
3. Find 2D Animation package and import “Samples” to the project
4. Open Boris.psd Sprite in Sprite Editor (Assets/Samples/2D Animation/15.0.3/Samples/1 Simple/Sprites/Boris.psd)
5. Change to “Skinning Editor” mode in Sprite Editor
6. Enable “Switch between Sprite sheet and Character mode” button
7. Select “Automatically generates mesh geometry” button
8. Press “Generate For All Visible” button in “Geometry” overlay menu
9. Observe the Console
Actual results: “Assertion failed
UnityEditor.GUIView:ProcessEvent (UnityEngine.EntityId,intptr,bool&) (at /Users/bokken/build/output/unity/unity/Editor/Mono/GUIView.cs:70)” error is thrown in the Console window when pressing “Generate For All Visible”
Expected results: No errors are thrown in the Console window when pressing “Generate For All Visible”
Reproducible with versions: 6000.0.74f1, 6000.3.14f1, 6000.4.5f1, 6000.5.0b6, 6000.6.0a4
Tested on (OS): macOS Silicon Tahoe 26.4.1