How to reproduce:
1. Open the attached 'project-1182792.zip' project
2. In the Project window select 'alembicCube.abc'
3. In the Inspector window modify 'Scale Factor' value

Expected result: multiple warning messages are logged in the Console window
Actual result: no warning messages are logged in the Console window

Reproducible with: 2019.2.0a6, 2019.2.7f2, 2019.3.0b5, 2020.1.0a6 (1.0.0, 1.0.5)
Not reproducible with: 2018.4.10f1, 2019.2.0a5 (1.0.0, 1.0.5)
Could not test with: 2017.4.32f1 (Package Manager not available)

Additional notes: editing 'Geometry' or 'Cameras' areas produces a different warning message than changing 'Scene' values

Modifying 'Scene': OnInspectorGUI should call serializedObject.Update() at its beginning and serializedObject.ApplyModifiedProperties() before calling ApplyRevertGUI() method.
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

Modifying 'Geometry' or 'Cameras': OnInspectorGUI should call serializedObject.Update() at its beginning and serializedObject.ApplyModifiedProperties() before calling ApplyRevertGUI() method.
UnityEditor.PopupCallbackInfo:SetEnumValueDelegate(Object, String[], Int32)