diff --git a/Packages/com.unity.inputsystem/CHANGELOG.md b/Packages/com.unity.inputsystem/CHANGELOG.md
index 10fd9c4724..6a9a909a41 100644
--- a/Packages/com.unity.inputsystem/CHANGELOG.md
+++ b/Packages/com.unity.inputsystem/CHANGELOG.md
@@ -12,6 +12,10 @@ however, it has to be formatted properly to pass verification tests.
 
 ### Fixed
 - Fixed an issue causing the Action context menu to not show on right click when right clicking an action in the Input Action Editor [ISXB-1134](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1134).
+- Fixed `ArgumentNullException: Value cannot be null.` during the migration of Project-wide Input Actions from `InputManager.asset` to `InputSystem_Actions.inputactions` asset which lead do the lost of the configuration [ISXB-1105](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1105)
+
+### Changed
+- Added back the InputManager to InputSystem project-wide asset migration code with performance improvement (ISX-2086)
 
 ## [1.11.2] - 2024-10-16
 
diff --git a/Packages/com.unity.inputsystem/InputSystem/Editor/ProjectWideActions/ProjectWideActionsAsset.cs b/Packages/com.unity.inputsystem/InputSystem/Editor/ProjectWideActions/ProjectWideActionsAsset.cs
index 027faf6e5f..848af6320a 100644
--- a/Packages/com.unity.inputsystem/InputSystem/Editor/ProjectWideActions/ProjectWideActionsAsset.cs
+++ b/Packages/com.unity.inputsystem/InputSystem/Editor/ProjectWideActions/ProjectWideActionsAsset.cs
@@ -17,14 +17,25 @@ internal static class ProjectWideActionsAsset
 
         internal static class ProjectSettingsProjectWideActionsAssetConverter
         {
+            private const string kAssetPathInputManager = "ProjectSettings/InputManager.asset";
+            private const string kAssetNameProjectWideInputActions = "ProjectWideInputActions";
+
             class ProjectSettingsPostprocessor : AssetPostprocessor
             {
+                private static bool migratedInputActionAssets = false;
+
 #if UNITY_2021_2_OR_NEWER
                 private static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths, bool didDomainReload)
 #else
                 private static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths)
 #endif
                 {
+                    if (!migratedInputActionAssets && importedAssets.Contains(kAssetPathInputManager))
+                    {
+                        MoveInputManagerAssetActionsToProjectWideInputActionAsset();
+                        migratedInputActionAssets = true;
+                    }
+
                     if (!Application.isPlaying)
                     {
                         // If the Library folder is deleted, InputSystem will fail to retrieve the assigned Project-wide Asset because this look-up occurs
@@ -35,6 +46,103 @@ private static void OnPostprocessAllAssets(string[] importedAssets, string[] del
                     }
                 }
             }
+
+            private static void MoveInputManagerAssetActionsToProjectWideInputActionAsset(bool allowRetry = true)
+            {
+                var objects = AssetDatabase.LoadAllAssetsAtPath(EditorHelpers.GetPhysicalPath(kAssetPathInputManager));
+                if (objects == null)
+                    return;
+
+                var inputActionsAssets = objects.Where(o => o != null && o.name == kAssetNameProjectWideInputActions && o is InputActionAsset);
+
+                if (!inputActionsAssets.Any()) return;
+
+                Debug.Log("Migrating Project-wide Input Actions from InputManager.asset to InputSystem_Actions.inputactions asset");
+
+                // workarround for serialization bug with ScriptableObject in ProjectSettings during reimporting all asset, it should not be null
+                if (allowRetry)
+                {
+                    foreach (InputActionAsset inputActionsAsset in inputActionsAssets)
+                    {
+                        if (inputActionsAsset.m_ActionMaps == null)
+                        {
+                            // unload asset to avoid serialization bug and will try again later
+                            Resources.UnloadAsset(inputActionsAsset);
+                            Debug.Log($"Unexpected null action map encounted during the migration, will try again once later");
+                            EditorApplication.delayCall += () => { MoveInputManagerAssetActionsToProjectWideInputActionAsset(allowRetry: false); };
+                            return;
+                        }
+                    }
+                }
+
+                foreach (InputActionAsset inputActionsAsset in inputActionsAssets)
+                {
+                    if (inputActionsAsset != default)
+                    {
+                        // sanity check to avoid saving a badly serialized asset or empty asset
+                        if (inputActionsAsset.m_ActionMaps.LengthSafe() == 0)
+                        {
+                            continue;
+                        }
+                        string path = ProjectWideActionsAsset.kDefaultAssetPath;
+
+                        if (File.Exists(EditorHelpers.GetPhysicalPath(path)))
+                        {
+                            // We already have a path containing inputactions, find a new unique filename
+                            //
+                            //  eg  Assets/InputSystem_Actions.inputactions ->
+                            //      Assets/InputSystem_Actions (1).inputactions ->
+                            //      Assets/InputSystem_Actions (2).inputactions ...
+                            //
+                            string[] files = Directory.GetFiles("Assets", "*.inputactions");
+                            List<string> names = new List<string>();
+                            for (int i = 0; i < files.Length; i++)
+                            {
+                                names.Add(System.IO.Path.GetFileNameWithoutExtension(files[i]));
+                            }
+                            string unique = ObjectNames.GetUniqueName(names.ToArray(), kDefaultAssetName);
+                            path = "Assets/" + unique + ".inputactions";
+                        }
+
+                        var json = inputActionsAsset.ToJson();
+                        InputActionAssetManager.SaveAsset(EditorHelpers.GetPhysicalPath(path), json);
+
+                        Debug.Log($"Migrated Project-wide Input Actions from '{kAssetPathInputManager}' to '{path}' asset");
+
+                        // Update current project-wide settings if needed (don't replace if already set to something else)
+                        //
+                        if (InputSystem.actions == null || InputSystem.actions.name == kAssetNameProjectWideInputActions)
+                        {
+                            InputSystem.actions = (InputActionAsset)AssetDatabase.LoadAssetAtPath(path, typeof(InputActionAsset));
+                            Debug.Log($"Loaded Project-wide Input Actions from '{path}' asset");
+                        }
+                    }
+                }
+
+
+                bool hasChanged = false;
+                // Handle deleting all InputActionAssets as older 1.8.0 pre release could create more than one project wide input asset in the file
+                foreach (var obj in objects)
+                {
+                    if (obj is InputActionReference)
+                    {
+                        var actionReference = obj as InputActionReference;
+                        AssetDatabase.RemoveObjectFromAsset(obj);
+                        Object.DestroyImmediate(actionReference);
+                        hasChanged = true;
+                    }
+                    else if (obj is InputActionAsset)
+                    {
+                        AssetDatabase.RemoveObjectFromAsset(obj);
+                        hasChanged = true;
+                    }
+                }
+
+                if (hasChanged == true)
+                {
+                    AssetDatabase.SaveAssets();
+                }
+            }
         }
 
         // Returns the default asset path for where to create project-wide actions asset.