diff --git a/.chronus/changes/tcgc-fix-lro-regression-2026-0-14-14-18-31.md b/.chronus/changes/tcgc-fix-lro-regression-2026-0-14-14-18-31.md
new file mode 100644
index 0000000000..bcd323b4bb
--- /dev/null
+++ b/.chronus/changes/tcgc-fix-lro-regression-2026-0-14-14-18-31.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+Refine diagnostic for LRO and paging metadata generation.
\ No newline at end of file
diff --git a/packages/typespec-client-generator-core/src/methods.ts b/packages/typespec-client-generator-core/src/methods.ts
index a9e0421417..9f9b490996 100644
--- a/packages/typespec-client-generator-core/src/methods.ts
+++ b/packages/typespec-client-generator-core/src/methods.ts
@@ -268,7 +268,7 @@ function getSdkPagingServiceMethod<TServiceOperation extends SdkServiceOperation
   } else {
     const markAsPageableInfo = getMarkAsPageable(context, operation);
     if (markAsPageableInfo) {
-      const itemsProperty = ignoreDiagnostics(
+      const itemsProperty = diagnostics.pipe(
         getSdkModelPropertyType(context, markAsPageableInfo.itemsProperty, operation),
       );
       // tcgc will let all paging method return a list of items
@@ -454,9 +454,9 @@ function getServiceMethodLroMetadata<TServiceOperation extends SdkServiceOperati
         return {
           kind: "pollingSuccessProperty",
           responseModel: getSdkModel(context, step.responseModel),
-          target: ignoreDiagnostics(getSdkModelPropertyType(context, step.target)),
+          target: diagnostics.pipe(getSdkModelPropertyType(context, step.target)),
           sourceProperty: step.sourceProperty
-            ? ignoreDiagnostics(getSdkModelPropertyType(context, step.sourceProperty))
+            ? diagnostics.pipe(getSdkModelPropertyType(context, step.sourceProperty))
             : undefined,
         };
       }
@@ -515,7 +515,8 @@ function getServiceMethodLroMetadata<TServiceOperation extends SdkServiceOperati
     }
     return {
       kind: "reference",
-      operation: diagnostics.pipe(getSdkBasicServiceMethod(context, reference.operation, client))
+      // since these operations may not be included in the client customization, we ignore diagnostics here
+      operation: ignoreDiagnostics(getSdkBasicServiceMethod(context, reference.operation, client))
         .operation,
       parameterMap: reference.parameterMap,
       parameters,
diff --git a/packages/typespec-client-generator-core/test/methods/lro.test.ts b/packages/typespec-client-generator-core/test/methods/lro.test.ts
index 5f0c9be4de..055c322910 100644
--- a/packages/typespec-client-generator-core/test/methods/lro.test.ts
+++ b/packages/typespec-client-generator-core/test/methods/lro.test.ts
@@ -1235,3 +1235,71 @@ describe("getLroMetadata", () => {
     );
   });
 });
+
+it("versioned LRO with customization", async () => {
+  const runnerWithCore = await createSdkTestRunner({
+    librariesToAdd: [AzureCoreTestLibrary],
+    autoUsings: ["Azure.Core", "Azure.Core.Traits"],
+    emitterName: "@azure-tools/typespec-java",
+  });
+  await runnerWithCore.compileWithCustomization(
+    `
+    @service
+    @versioned(Versions)
+    namespace TestService;
+
+    enum Versions {
+      v1,
+      v2,
+    }
+
+    alias TestOperations = ResourceOperations<NoConditionalRequests & NoClientRequestId & NoRepeatableRequests>;
+
+    @resource("id")
+    model TestResult {
+      @key
+      id: string;
+
+      @lroStatus
+      status: JobStatus;
+    }
+
+    @lroStatus
+    union JobStatus {
+      string,
+      NotStarted: "notStarted",
+      Running: "running",
+
+      @lroSucceeded
+      Succeeded: "succeeded",
+
+      @lroFailed
+      Failed: "failed",
+
+      Canceled: "canceled",
+    }
+
+    @get
+    op get is TestOperations.ResourceRead<TestResult>;
+
+    @pollingOperation(get)
+    op create is TestOperations.LongRunningResourceCreateOrReplace<TestResult>;
+    `,
+    `
+    @client({
+      service: TestService,
+    })
+    namespace TestClient;
+      
+    op test is TestService.create;
+    `,
+  );
+  strictEqual(runnerWithCore.context.diagnostics.length, 0);
+  const client = runnerWithCore.context.sdkPackage.clients[0];
+  strictEqual(client.methods.length, 1);
+  const method = client.methods[0];
+  strictEqual(method.name, "test");
+  strictEqual(method.kind, "lro");
+  const lroMetadata = method.lroMetadata;
+  ok(lroMetadata);
+});