diff --git a/packages/next/src/client/components/errors/stitched-error.ts b/packages/next/src/client/components/errors/stitched-error.ts
index e4da4fe4869e2..45cfe96096a83 100644
--- a/packages/next/src/client/components/errors/stitched-error.ts
+++ b/packages/next/src/client/components/errors/stitched-error.ts
@@ -34,6 +34,9 @@ export function getReactStitchedError<T = unknown>(err: T): Error | T {
 }
 
 function appendOwnerStack(error: Error) {
+  if (!React.captureOwnerStack) {
+    return
+  }
   let stack = error.stack || ''
   // This module is only bundled in development mode so this is safe.
   const ownerStack = React.captureOwnerStack()
diff --git a/packages/next/src/client/components/errors/use-error-handler.ts b/packages/next/src/client/components/errors/use-error-handler.ts
index 4b681fb347551..6a40f1b7135c4 100644
--- a/packages/next/src/client/components/errors/use-error-handler.ts
+++ b/packages/next/src/client/components/errors/use-error-handler.ts
@@ -70,8 +70,8 @@ export function useErrorHandler(
       )
 
       // Reset error queues.
-      errorQueue.splice(0, 0)
-      rejectionQueue.splice(0, 0)
+      errorQueue.splice(0, errorQueue.length)
+      rejectionQueue.splice(0, rejectionQueue.length)
     }
   }, [handleOnUnhandledError, handleOnUnhandledRejection])
 }
diff --git a/packages/next/src/client/components/react-dev-overlay/_experimental/internal/container/runtime-error/use-error-hook.ts b/packages/next/src/client/components/react-dev-overlay/_experimental/internal/container/runtime-error/use-error-hook.ts
index 3b0fb084bfb18..7b05b69064a50 100644
--- a/packages/next/src/client/components/react-dev-overlay/_experimental/internal/container/runtime-error/use-error-hook.ts
+++ b/packages/next/src/client/components/react-dev-overlay/_experimental/internal/container/runtime-error/use-error-hook.ts
@@ -26,12 +26,12 @@ function getErrorSignature(ev: SupportedErrorEvent): string {
     case ACTION_UNHANDLED_REJECTION: {
       return `${event.reason.name}::${event.reason.message}::${event.reason.stack}`
     }
-    default: {
-    }
+    default:
+      break
   }
 
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  const _: never = event as never
+  const _ = event satisfies never
   return ''
 }
 
diff --git a/packages/next/src/client/components/react-dev-overlay/internal/container/Errors.tsx b/packages/next/src/client/components/react-dev-overlay/internal/container/Errors.tsx
index c46ac62bc2198..c62dacdd91406 100644
--- a/packages/next/src/client/components/react-dev-overlay/internal/container/Errors.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/internal/container/Errors.tsx
@@ -236,6 +236,7 @@ export function Errors({
     return (
       <Toast
         data-nextjs-toast
+        data-issues
         className={`nextjs-toast-errors-parent${hasStaticIndicator ? ' nextjs-error-with-static' : ''}`}
         onClick={fullscreen}
       >
@@ -256,7 +257,8 @@ export function Errors({
             <line x1="12" y1="16" x2="12.01" y2="16"></line>
           </svg>
           <span>
-            {readyErrors.length} issue{readyErrors.length > 1 ? 's' : ''}
+            <span data-issues-count>{readyErrors.length}</span> issue
+            {readyErrors.length > 1 ? 's' : ''}
           </span>
           <button
             data-nextjs-toast-errors-hide-button
diff --git a/packages/next/src/client/components/react-dev-overlay/shared.ts b/packages/next/src/client/components/react-dev-overlay/shared.ts
index 77540bb7e6baa..5cf4dce52e374 100644
--- a/packages/next/src/client/components/react-dev-overlay/shared.ts
+++ b/packages/next/src/client/components/react-dev-overlay/shared.ts
@@ -94,7 +94,7 @@ function pushErrorFilterDuplicates(
   return [
     ...errors.filter((e) => {
       // Filter out duplicate errors
-      return e.event.reason !== err.event.reason
+      return e.event.reason.stack !== err.event.reason.stack
     }),
     err,
   ]
diff --git a/test/development/app-dir/dynamic-io-dev-errors/dynamic-io-dev-errors.test.ts b/test/development/app-dir/dynamic-io-dev-errors/dynamic-io-dev-errors.test.ts
index bad7d0c15cecb..f115b8acf3779 100644
--- a/test/development/app-dir/dynamic-io-dev-errors/dynamic-io-dev-errors.test.ts
+++ b/test/development/app-dir/dynamic-io-dev-errors/dynamic-io-dev-errors.test.ts
@@ -32,7 +32,9 @@ describe('Dynamic IO Dev Errors', () => {
   it('should show a red box error on client navigations', async () => {
     const browser = await next.browser('/no-error')
 
-    expect(await hasErrorToast(browser)).toBe(false)
+    await retry(async () => {
+      expect(await hasErrorToast(browser)).toBe(false)
+    })
 
     await browser.elementByCss("[href='/error']").click()
 
diff --git a/test/development/app-dir/hydration-error-count/app/bad-nesting/page.tsx b/test/development/app-dir/hydration-error-count/app/bad-nesting/page.tsx
new file mode 100644
index 0000000000000..7dd2402076b23
--- /dev/null
+++ b/test/development/app-dir/hydration-error-count/app/bad-nesting/page.tsx
@@ -0,0 +1,7 @@
+export default function Page() {
+  return (
+    <p>
+      <p>nest</p>
+    </p>
+  )
+}
diff --git a/test/development/app-dir/hydration-error-count/app/html-diff/page.tsx b/test/development/app-dir/hydration-error-count/app/html-diff/page.tsx
new file mode 100644
index 0000000000000..57acfd0c3aacf
--- /dev/null
+++ b/test/development/app-dir/hydration-error-count/app/html-diff/page.tsx
@@ -0,0 +1,5 @@
+'use client'
+
+export default function Page() {
+  return <p>{typeof window === 'undefined' ? 'server' : 'client'}</p>
+}
diff --git a/test/development/app-dir/hydration-error-count/app/layout.tsx b/test/development/app-dir/hydration-error-count/app/layout.tsx
new file mode 100644
index 0000000000000..888614deda3ba
--- /dev/null
+++ b/test/development/app-dir/hydration-error-count/app/layout.tsx
@@ -0,0 +1,8 @@
+import { ReactNode } from 'react'
+export default function Root({ children }: { children: ReactNode }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}
diff --git a/test/development/app-dir/hydration-error-count/hydration-error-count.test.ts b/test/development/app-dir/hydration-error-count/hydration-error-count.test.ts
new file mode 100644
index 0000000000000..54442ffe8a340
--- /dev/null
+++ b/test/development/app-dir/hydration-error-count/hydration-error-count.test.ts
@@ -0,0 +1,33 @@
+import { nextTestSetup } from 'e2e-utils'
+import { hasErrorToast, getToastErrorCount, retry } from 'next-test-utils'
+
+describe('hydration-error-count', () => {
+  const { next } = nextTestSetup({
+    files: __dirname,
+  })
+
+  // These error count should be consistent between normal mode and when reactOwnerStack is enabled (PPR testing)
+  it('should have correct hydration error count for bad nesting', async () => {
+    const browser = await next.browser('/bad-nesting')
+
+    await retry(async () => {
+      await hasErrorToast(browser)
+      const totalErrorCount = await getToastErrorCount(browser)
+
+      // One hydration error and one warning
+      expect(totalErrorCount).toBe(2)
+    })
+  })
+
+  it('should have correct hydration error count for html diff', async () => {
+    const browser = await next.browser('/html-diff')
+
+    await retry(async () => {
+      await hasErrorToast(browser)
+      const totalErrorCount = await getToastErrorCount(browser)
+
+      // One hydration error and one warning
+      expect(totalErrorCount).toBe(1)
+    })
+  })
+})
diff --git a/test/development/app-dir/hydration-error-count/next.config.js b/test/development/app-dir/hydration-error-count/next.config.js
new file mode 100644
index 0000000000000..807126e4cf0bf
--- /dev/null
+++ b/test/development/app-dir/hydration-error-count/next.config.js
@@ -0,0 +1,6 @@
+/**
+ * @type {import('next').NextConfig}
+ */
+const nextConfig = {}
+
+module.exports = nextConfig
diff --git a/test/lib/next-test-utils.ts b/test/lib/next-test-utils.ts
index e2a660a6ab3f7..365372b8aea8e 100644
--- a/test/lib/next-test-utils.ts
+++ b/test/lib/next-test-utils.ts
@@ -887,17 +887,32 @@ export async function assertNoRedbox(browser: BrowserInterface) {
 export async function hasErrorToast(
   browser: BrowserInterface
 ): Promise<boolean> {
-  return (
+  return Boolean(
+    await browser.eval(() => {
+      const portal = [].slice
+        .call(document.querySelectorAll('nextjs-portal'))
+        .find((p) => p.shadowRoot.querySelector('[data-issues]'))
+
+      const root = portal?.shadowRoot
+      const node = root?.querySelector('[data-issues-count]')
+      return !!node
+    })
+  )
+}
+
+export async function getToastErrorCount(
+  browser: BrowserInterface
+): Promise<number> {
+  return parseInt(
     (await browser.eval(() => {
-      return Boolean(
-        [].slice.call(document.querySelectorAll('nextjs-portal')).find((p) =>
-          p.shadowRoot.querySelector(
-            // TODO(jiwon): data-nextjs-toast may not be an error indicator in new UI
-            isNewDevOverlay ? '[data-issues]' : '[data-nextjs-toast]'
-          )
-        )
-      )
-    })) ?? false // When browser.eval() throws, it returns null.
+      const portal = [].slice
+        .call(document.querySelectorAll('nextjs-portal'))
+        .find((p) => p.shadowRoot.querySelector('[data-issues]'))
+
+      const root = portal?.shadowRoot
+      const node = root?.querySelector('[data-issues-count]')
+      return node?.innerText || '0'
+    })) ?? 0
   )
 }