diff --git a/assets/js/services/local-storage.js b/assets/js/services/local-storage.js
index 8efccde126..22b778733a 100644
--- a/assets/js/services/local-storage.js
+++ b/assets/js/services/local-storage.js
@@ -117,7 +117,10 @@ function getInfluxDBUrls() {
     initializeStorageItem('urls', JSON.stringify(DEFAULT_STORAGE_URLS));
   }
 
-  return JSON.parse(localStorage.getItem(urlStorageKey));
+  const storedUrls = JSON.parse(localStorage.getItem(urlStorageKey));
+  // Backfill any new default keys missing from stored data (e.g., when new
+  // products like core/enterprise are added after a user's first visit).
+  return { ...DEFAULT_STORAGE_URLS, ...storedUrls };
 }
 
 // Get the current or previous URL for a specific product or a custom url
@@ -131,8 +134,8 @@ function getInfluxDBUrl(product) {
   const urlsString = localStorage.getItem(urlStorageKey);
   const urlsObj = JSON.parse(urlsString);
 
-  // Return the URL of the specified product
-  return urlsObj[product];
+  // Return the URL of the specified product, falling back to the default
+  return urlsObj[product] ?? DEFAULT_STORAGE_URLS[product];
 }
 
 /*
diff --git a/cypress/e2e/influxdb-url.cy.js b/cypress/e2e/influxdb-url.cy.js
new file mode 100644
index 0000000000..7203e69d8b
--- /dev/null
+++ b/cypress/e2e/influxdb-url.cy.js
@@ -0,0 +1,80 @@
+/// <reference types="cypress" />
+
+/**
+ * InfluxDB URL localStorage E2E Test Suite
+ *
+ * Tests that the InfluxDB URL replacement logic in influxdb-url.js handles
+ * localStorage correctly, including stale data from returning visitors.
+ *
+ * Regression tests for https://github.com/influxdata/docs-v2/issues/6960
+ * where stale localStorage missing the `core` key caused JavaScript to
+ * replace rendered hostnames with "undefined" in code blocks.
+ */
+
+const STORAGE_KEY = 'influxdata_docs_urls';
+const TEST_PAGE = '/influxdb3/core/plugins/';
+const EXPECTED_PRODUCT_KEYS = [
+  'oss',
+  'cloud',
+  'core',
+  'enterprise',
+  'serverless',
+  'dedicated',
+  'clustered',
+];
+
+describe('InfluxDB URL - localStorage', function () {
+  it('should not render "undefined" in code blocks when localStorage is missing product keys', function () {
+    // Simulate a returning visitor whose localStorage was created before
+    // core/enterprise products were added — missing those keys entirely.
+    const staleUrls = {
+      oss: 'http://localhost:8086',
+      cloud: 'https://us-west-2-1.aws.cloud2.influxdata.com',
+      prev_oss: 'http://localhost:8086',
+      prev_cloud: 'https://us-west-2-1.aws.cloud2.influxdata.com',
+      custom: '',
+    };
+
+    cy.visit(TEST_PAGE, {
+      onBeforeLoad(win) {
+        win.localStorage.setItem(STORAGE_KEY, JSON.stringify(staleUrls));
+      },
+    });
+
+    // The api-endpoint block should show the default Core host, not "undefined"
+    cy.get('.article--content pre.api-endpoint')
+      .first()
+      .should('contain', 'localhost:8181')
+      .and('not.contain', 'undefined');
+
+    // No code block in the article should contain "undefined" as a bare host
+    cy.get('.article--content pre:not(.preserve)').each(($el) => {
+      cy.wrap($el).invoke('text').should('not.match', /undefined\/api\//);
+    });
+  });
+
+  it('should backfill all expected product URL keys into localStorage', function () {
+    cy.visit(TEST_PAGE, {
+      onBeforeLoad(win) {
+        // Start with no stored URLs — forces initialization
+        win.localStorage.removeItem(STORAGE_KEY);
+      },
+    });
+
+    // After the page loads and JS initializes, localStorage should contain
+    // all expected product keys with non-empty URL values.
+    cy.window().then((win) => {
+      const stored = JSON.parse(win.localStorage.getItem(STORAGE_KEY));
+      expect(stored).to.be.an('object');
+
+      EXPECTED_PRODUCT_KEYS.forEach((key) => {
+        expect(stored, `stored URLs should have key "${key}"`).to.have.property(
+          key
+        );
+        expect(stored[key], `"${key}" should be a non-empty string`).to.be.a(
+          'string'
+        ).and.not.be.empty;
+      });
+    });
+  });
+});