Misaki Hm.. I created a new Unity project and the issue doesn't occur there..
It's strange because I have no issues like this with with any other assets in the main project.
I just noticed that whenever I select a SkeletonData asset in Unity in the main project, this error is logged:
NullReferenceException: Object reference not set to an instance of an object
Spine.Unity.Editor.SkeletonDataAssetInspector.HandleAtlasAssetsNulls () (at Assets/Spine/Editor/spine-unity/Editor/Asset Types/SkeletonDataAssetInspector.cs:386)
Spine.Unity.Editor.SkeletonDataAssetInspector.OnInspectorGUI () (at Assets/Spine/Editor/spine-unity/Editor/Asset Types/SkeletonDataAssetInspector.cs:192)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass71_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <d92715ccd3ac42dbaeb8a2239166e2e8>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)
I updated the Spine Unity Package and the issue seems to be resolved.
I had checked the changelog before posting this question and I didn't see anything about this issue in the notes here: http://en.esotericsoftware.com/spine-changelog#v4-1-18
Is there another place I should look for the changelog in the future?
Old Package version: spine-unity-4.1-2022-12-19.unitypackage
New Package version: spine-unity-4.1-2023-02-17.unitypackage