diff --git a/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/MaterialInstanceGenerator.cpp b/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/MaterialInstanceGenerator.cpp
index 86464fe..dac8331 100644
--- a/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/MaterialInstanceGenerator.cpp
+++ b/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/MaterialInstanceGenerator.cpp
@@ -98,6 +98,11 @@ void UMaterialInstanceGenerator::PreFinishAssetGeneration() {
 	const TSharedPtr<FJsonValue> AssetUserDataJson = AssetObjectProperties->GetField<EJson::Array>(TEXT("AssetUserData"));
 	
 	GetPropertySerializer()->DeserializePropertyValue(AssetUserDataProperty, AssetUserDataJson.ToSharedRef(), AssetUserData);
+
+	// AssetUserData is deserialized in PRE_FINSHED, after the
+	// DATA_POPULATION save. Without marking the asset changed the package is not re-saved and the
+	// AssetUserData written here is lost (IsSimpleAssetUpToDate then fails on every re-run).
+	MarkAssetChanged();
 }
 
 void EnsureStaticSwitchNodesPresent(UMaterial* Material, const FStaticParameterSet& StaticParameters) {
diff --git a/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/SimpleAssetGenerator.cpp b/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/SimpleAssetGenerator.cpp
index e7e908a..93358b4 100644
--- a/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/SimpleAssetGenerator.cpp
+++ b/AssetGenerator/Source/AssetGenerator/Private/Toolkit/AssetTypeGenerator/SimpleAssetGenerator.cpp
@@ -16,6 +16,16 @@ void USimpleAssetGenerator::PopulateAssetWithData() {
 		UE_LOG(LogAssetGenerator, Display, TEXT("%s %s is not up to date, regenerating data"), *ExistingAssetObject->GetClass()->GetName(), *ExistingAssetObject->GetPathName());
 		
 		PopulateSimpleAssetWithData(ExistingAssetObject);
+
+		// Commit d665fd6 ("Update to UE 5.6.1")
+		// moved data population out of CreateAssetPackage() (CONSTRUCTION, which always marks
+		// the asset changed) into this DATA_POPULATION stage, but never marks the asset as
+		// changed here. UAssetTypeGenerator::AdvanceGenerationState only saves when
+		// bAssetChanged is set, and the property serializer does not dirty the package, so
+		// every simple asset (MaterialInstance, PhysicalMaterial, MPC, DataAsset, curves...)
+		// was written to disk as the empty CONSTRUCTION shell and the populated data was lost.
+		// Marking the asset changed makes AdvanceGenerationState save the populated package.
+		MarkAssetChanged();
 	}
 }