diff --git a/ui/src/components/ProcessDiagram/ProcessDiagram.tsx b/ui/src/components/ProcessDiagram/ProcessDiagram.tsx
index 30fa88f1..05b47e94 100644
--- a/ui/src/components/ProcessDiagram/ProcessDiagram.tsx
+++ b/ui/src/components/ProcessDiagram/ProcessDiagram.tsx
@@ -69,8 +69,12 @@ export function ProcessDiagram({
 
   const currentRouteId = routeStack[routeStack.length - 1];
 
+  // Only use the pre-fetched diagramLayout for the root route.
+  // When drilled down into a sub-route, fetch the sub-route's diagram by route ID.
+  const effectiveLayout = currentRouteId === routeId ? diagramLayout : undefined;
+
   const { sections, totalWidth, totalHeight, isLoading, error } = useDiagramData(
-    application, currentRouteId, direction, diagramLayout,
+    application, currentRouteId, direction, effectiveLayout,
   );
 
   // Collect ENDPOINT node IDs — these are always "traversed" when overlay is active