Each stage should only respond to its own stage invalidation notices.

lib/mayaHydra/hydraExtensions/sceneIndex/mhMayaUsdProxyShapeSceneIndex.cpp

@@ -103,6 +103,18 @@ void MayaUsdProxyShapeSceneIndex::_StageSet(const MAYAUSDAPI_NS::ProxyStageSetNo
 // In these cases we set the stage to null and start over.
 void MayaUsdProxyShapeSceneIndex::_StageInvalidate(const MAYAUSDAPI_NS::ProxyStageInvalidateNotice& notice) 
 { 
+    constexpr char const* INVALID_PROXY_SHAPE_MSG = 
+        "Stage invalidate notification for invalid proxy shape node at path %s";
+
+    if (!TF_VERIFY(_dagNodeHandle.isValid(), INVALID_PROXY_SHAPE_MSG, notice.GetProxyShapePath().data())) {
+        return;
+    }
+
+    // Is the notification for us?
+    if (notice.GetProxyShapeObj() != _dagNodeHandle.object()) {
+        return;
+    }
+
     _usdImagingStageSceneIndex->SetStage(nullptr);
     _populated = false;
     // Simply mark populate as dirty and do not call

test/lib/mayaUsd/render/mayaToHydra/CMakeLists.txt

@@ -80,6 +80,7 @@ set(INTERACTIVE_TEST_SCRIPT_FILES
     cpp/testGeomSubsetsPicking.py
     cpp/testSinglePicking.py
     cpp/testSceneIndexDirtying.py
+    cpp/testUsdStageInvalidate.py
     cpp/testGeomSubsetsWireframeHighlight.py
 )
 

test/lib/mayaUsd/render/mayaToHydra/cpp/CMakeLists.txt

@@ -46,6 +46,7 @@ target_sources(${TARGET_NAME}
         testGeomSubsetsPicking.cpp
         testSinglePicking.cpp
         testSceneIndexDirtying.cpp
+        testUsdStageInvalidate.cpp
         testGeomSubsetsWireframeHighlight.cpp
 )
 

test/lib/mayaUsd/render/mayaToHydra/cpp/testUsdStageInvalidate.cpp

@@ -0,0 +1,46 @@
+// Copyright 2023 Autodesk
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "testUtils.h"
+
+#include <maya/MGlobal.h>
+
+#include <gtest/gtest.h>
+
+PXR_NAMESPACE_USING_DIRECTIVE
+
+TEST(TestUsdStageInvalidate, testAddStage)
+{
+    // Setup notifications accumulator for the first terminal scene index
+    const SceneIndicesVector& sceneIndices = GetTerminalSceneIndices();
+    ASSERT_GT(sceneIndices.size(), 0u);
+    auto siRoot = sceneIndices.front();
+
+    // Start accumulating notifications.
+    SceneIndexNotificationsAccumulator notifsAccumulator(siRoot);
+
+    // Add a stage with new layer.
+    MGlobal::executePythonCommand("import mayaUsd_createStageWithNewLayer; mayaUsd_createStageWithNewLayer.createStageWithNewLayer()");
+
+    // Confirm the new stage is in the Hydra scene.
+    auto prim = siRoot->GetPrim(SdfPath("/MayaUsdProxyShape_PluginNode/mayaUsdProxyShape1"));
+    ASSERT_TRUE(prim.dataSource);
+
+    // There should not have been any prim removed notifications, only prim
+    // added and dirtied.
+    ASSERT_EQ(notifsAccumulator.GetRemovedPrimEntries().size(), 0u);
+    ASSERT_GT(notifsAccumulator.GetDirtiedPrimEntries().size(), 0u);
+    ASSERT_GT(notifsAccumulator.GetAddedPrimEntries().size(), 0u);
+}

test/lib/mayaUsd/render/mayaToHydra/cpp/testUsdStageInvalidate.py

@@ -0,0 +1,43 @@
+# Copyright 2024 Autodesk
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import maya.cmds as cmds
+import fixturesUtils
+import mtohUtils
+import usdUtils
+import testUtils
+from testUtils import PluginLoaded
+
+class TestUsdStageInvalidate(mtohUtils.MayaHydraBaseTestCase):
+    # MayaHydraBaseTestCase.setUpClass requirement.
+    _file = __file__
+
+    # Base class setUp() defines HdStorm as the renderer.
+
+    def setupScene(self):
+        usdScenePath = testUtils.getTestScene('testUsdNativeInstances', 'instancedCubeHierarchies.usda')
+        usdUtils.createStageFromFile(usdScenePath)
+        # Clear the selection, otherwise we'll get selection highlighting
+        # geometry prim removals for the current stage when we create and
+        # switch the selection to the new stage in the C++ part of the test.
+        cmds.select(clear=True)
+        cmds.refresh()
+
+    def test_addStage(self):
+        self.setupScene()
+        with PluginLoaded('mayaHydraCppTests'):
+            cmds.mayaHydraCppTest(f="TestUsdStageInvalidate.testAddStage")
+
+if __name__ == '__main__':
+    fixturesUtils.runTests(globals())