diff --git a/packages/core/src/RenderingEngine/BaseRenderingEngine.ts b/packages/core/src/RenderingEngine/BaseRenderingEngine.ts
index 5ecae8e570..c7fc461182 100644
--- a/packages/core/src/RenderingEngine/BaseRenderingEngine.ts
+++ b/packages/core/src/RenderingEngine/BaseRenderingEngine.ts
@@ -16,6 +16,7 @@ import {
 import type IStackViewport from '../types/IStackViewport';
 import type IVolumeViewport from '../types/IVolumeViewport';
 import viewportTypeToViewportClass from './helpers/viewportTypeToViewportClass';
+import ViewportStatus from '../enums/ViewportStatus';
 
 import type * as EventTypes from '../types/EventTypes';
 import type {
@@ -689,6 +690,10 @@ abstract class BaseRenderingEngine {
     // Add the viewports to the set of flagged viewports
     viewportIds.forEach((viewportId) => {
       this._needsRender.add(viewportId);
+      const viewport = this._viewports.get(viewportId);
+      if (viewport) {
+        viewport.viewportStatus = ViewportStatus.NEEDS_RENDER;
+      }
     });
 
     // Render any flagged viewports
diff --git a/packages/core/src/RenderingEngine/ECGViewport.ts b/packages/core/src/RenderingEngine/ECGViewport.ts
index f0317e5125..1ee99f2bd6 100644
--- a/packages/core/src/RenderingEngine/ECGViewport.ts
+++ b/packages/core/src/RenderingEngine/ECGViewport.ts
@@ -634,6 +634,7 @@ class ECGViewport extends Viewport {
     this.drawLabels(ctx, layouts);
 
     ctx.resetTransform();
+    this.setRendered();
 
     triggerEvent(this.element, EVENTS.IMAGE_RENDERED, {
       element: this.element,
diff --git a/packages/core/src/RenderingEngine/VideoViewport.ts b/packages/core/src/RenderingEngine/VideoViewport.ts
index 385bb63a2e..639c05ade1 100644
--- a/packages/core/src/RenderingEngine/VideoViewport.ts
+++ b/packages/core/src/RenderingEngine/VideoViewport.ts
@@ -1185,6 +1185,7 @@ class VideoViewport extends Viewport {
       (actor.actor as ICanvasActor).render(this, this.canvasContext);
     }
     this.canvasContext.resetTransform();
+    this.setRendered();
 
     // This is stack new image to agree with stack/non-volume viewports
     triggerEvent(this.element, EVENTS.STACK_NEW_IMAGE, {
diff --git a/packages/core/src/RenderingEngine/Viewport.ts b/packages/core/src/RenderingEngine/Viewport.ts
index 1fedee84f0..d9de46796e 100644
--- a/packages/core/src/RenderingEngine/Viewport.ts
+++ b/packages/core/src/RenderingEngine/Viewport.ts
@@ -250,6 +250,14 @@ class Viewport {
     this.viewportStatus = ViewportStatus.RENDERED;
   }
 
+  /**
+   * Mark the viewport as needing a render pass (e.g. after external display-set / segmentation updates).
+   * Does not queue a render; the rendering engine’s normal RAF cycle will pick this up.
+   */
+  public setNeedsRender(): void {
+    this.viewportStatus = ViewportStatus.NEEDS_RENDER;
+  }
+
   /**
    *  This applies a color transform as an svg filter to the output image.
    */
diff --git a/packages/core/src/enums/ViewportStatus.ts b/packages/core/src/enums/ViewportStatus.ts
index 9af71df641..ca92ff51bc 100644
--- a/packages/core/src/enums/ViewportStatus.ts
+++ b/packages/core/src/enums/ViewportStatus.ts
@@ -5,6 +5,8 @@ enum ViewportStatus {
   LOADING = 'loading',
   /** Ready to be rendered */
   PRE_RENDER = 'preRender',
+  /** Render has been requested and is pending in RAF queue */
+  NEEDS_RENDER = 'needsRender',
   /** In the midst of a resize */
   RESIZE = 'resize',
   /** Rendered image data */
diff --git a/packages/tools/src/utilities/segmentation/utilsForWorker.ts b/packages/tools/src/utilities/segmentation/utilsForWorker.ts
index 2726c0d635..f9f2467550 100644
--- a/packages/tools/src/utilities/segmentation/utilsForWorker.ts
+++ b/packages/tools/src/utilities/segmentation/utilsForWorker.ts
@@ -39,6 +39,14 @@ export const getSegmentationDataForWorker = (
   segmentIndices
 ) => {
   const segmentation = getSegmentation(segmentationId);
+  if (!segmentation?.representationData) {
+    console.debug(
+      'getSegmentationDataForWorker: segmentation missing or not ready',
+      segmentationId
+    );
+    return null;
+  }
+
   const { representationData } = segmentation;
 
   const { Labelmap } = representationData;
diff --git a/tests/labelmapsegmentationtools.spec.ts b/tests/labelmapsegmentationtools.spec.ts
index 7189c32367..468a1eb6a6 100644
--- a/tests/labelmapsegmentationtools.spec.ts
+++ b/tests/labelmapsegmentationtools.spec.ts
@@ -4,10 +4,11 @@ import {
   checkForScreenshot,
   screenShotPaths,
   simulateClicksOnElement,
+  waitForViewportsRendered,
 } from './utils/index';
 
 const delayBetweenClicks = async (page: any) => {
-  await page.waitForTimeout(1500);
+  await waitForViewportsRendered(page);
 };
 
 test.beforeEach(async ({ page }) => {
@@ -621,7 +622,7 @@ test.describe('Basic manual labelmap Segmentation tools', async () => {
       ],
     });
 
-    await page.waitForTimeout(3000);
+    await waitForViewportsRendered(page);
     await checkForScreenshot(
       page,
       screenshotLocator,
@@ -682,7 +683,7 @@ test.describe('Basic manual labelmap Segmentation tools', async () => {
       ],
     });
 
-    await page.waitForTimeout(3000);
+    await waitForViewportsRendered(page);
     await checkForScreenshot(
       page,
       screenshotLocator,
diff --git a/tests/utils/index.ts b/tests/utils/index.ts
index bb02070d26..d8551e5f98 100644
--- a/tests/utils/index.ts
+++ b/tests/utils/index.ts
@@ -6,3 +6,4 @@ export { simulateClicksOnElement } from './simulateClicksOnElement';
 export { simulateDrawPath } from './simulateDrawPath';
 export { reduceViewportsSize } from './reduceViewportsSize';
 export { attemptAction } from './attemptAction';
+export { waitForViewportsRendered } from './waitForViewportsRendered';
diff --git a/tests/utils/waitForViewportsRendered.ts b/tests/utils/waitForViewportsRendered.ts
new file mode 100644
index 0000000000..4086c1bf7a
--- /dev/null
+++ b/tests/utils/waitForViewportsRendered.ts
@@ -0,0 +1,94 @@
+import type { Page } from '@playwright/test';
+
+type WaitForViewportsRenderedOptions = {
+  timeout?: number;
+  /**
+   * If true (default), also waits for any volume actors referenced by the
+   * viewports to report loaded.
+   */
+  waitVolumeLoad?: boolean;
+};
+
+/**
+ * Stabilize tests by waiting for a short tick, network idle, then viewport render completion.
+ * To use this method safely, you may need to make changes to OHIF and/or CS3D
+ * methods handling clicks (SHOULD be commands modules only).  These should set the
+ * state to needs render synchronously so that this method can safely wait for the render to complete.
+ * Examples such as changing the hanging protocol currently don't set such a state
+ * and thus can't be rendered without a delay.
+ * 
+ * If options.waitVolumeLoad is not false, then this method will wait for all volumes
+ * associated with viewports to be loaded.
+ */
+export const waitForViewportsRendered = async (
+  page: Page,
+  options: WaitForViewportsRenderedOptions = {}
+) => {
+  const { timeout = 15000, waitVolumeLoad = true } = options;
+
+  await page.waitForFunction(
+    ({ waitVolumeLoad }) => {
+      const cornerstone = (window as any).cornerstone;
+      if (!cornerstone?.getRenderingEngines) {
+        return false;
+      }
+
+      const renderingEngines = cornerstone.getRenderingEngines();
+      const viewports = renderingEngines.flatMap((engine) =>
+        engine.getViewports ? engine.getViewports() : []
+      );
+
+      if (!viewports.length) {
+        return false;
+      }
+
+      const allRendered = viewports.every(
+        (viewport) => viewport?.viewportStatus === 'rendered'
+      );
+
+      if (!allRendered) {
+        return false;
+      }
+
+      if (!waitVolumeLoad) {
+        return true;
+      }
+
+      const cache = cornerstone.cache;
+      if (!cache?.getVolume) {
+        return true;
+      }
+
+      const actorEntries = viewports.flatMap((viewport) =>
+        viewport?.getActors ? viewport.getActors() : []
+      );
+
+      for (const actorEntry of actorEntries) {
+        const id = actorEntry?.referencedId || actorEntry?.uid;
+        if (!id) {
+          continue;
+        }
+
+        let volume: any;
+        try {
+          volume = cache.getVolume(id);
+        } catch {
+          continue;
+        }
+
+        const loaded =
+          volume?.loadStatus && typeof volume.loadStatus.loaded === 'boolean'
+            ? volume.loadStatus.loaded
+            : true;
+
+        if (!loaded) {
+          return false;
+        }
+      }
+
+      return true;
+    },
+    { waitVolumeLoad },
+    { timeout }
+  );
+};