diff --git a/packages/router-core/src/ssr/transformStreamWithRouter.ts b/packages/router-core/src/ssr/transformStreamWithRouter.ts
index 8322b8da88..9dc91996c5 100644
--- a/packages/router-core/src/ssr/transformStreamWithRouter.ts
+++ b/packages/router-core/src/ssr/transformStreamWithRouter.ts
@@ -65,6 +65,7 @@ function createPassthrough(onCancel?: () => void) {
       res.destroyed = true
     },
     destroy: (error) => {
+      res.destroyed = true
       controller.error(error)
     },
     destroyed: false,
@@ -81,8 +82,8 @@ async function readStream(
     onError?: (error: unknown) => void
   },
 ) {
+  const reader = stream.getReader()
   try {
-    const reader = stream.getReader()
     let chunk
     while (!(chunk = await reader.read()).done) {
       opts.onData?.(chunk)
@@ -90,6 +91,8 @@ async function readStream(
     opts.onEnd?.()
   } catch (error) {
     opts.onError?.(error)
+  } finally {
+    reader.releaseLock()
   }
 }
 
@@ -112,10 +115,10 @@ export function transformStreamWithRouter(
   })
   const textDecoder = new TextDecoder()
 
-  let isAppRendering = true as boolean
+  let isAppRendering = true
   let routerStreamBuffer = ''
   let pendingClosingTags = ''
-  let streamBarrierLifted = false as boolean
+  let streamBarrierLifted = false
   let leftover = ''
   let leftoverHtml = ''
 
@@ -151,13 +154,22 @@ export function transformStreamWithRouter(
 
       promise
         .then((html) => {
+          // Don't write to destroyed stream
+          if (finalPassThrough.destroyed) {
+            return
+          }
           if (isAppRendering) {
             routerStreamBuffer += html
           } else {
             finalPassThrough.write(html)
           }
         })
-        .catch(injectedHtmlDonePromise.reject)
+        .catch((err) => {
+          // Only reject if not already settled
+          if (!finalPassThrough.destroyed) {
+            injectedHtmlDonePromise.reject(err)
+          }
+        })
         .finally(() => {
           processingCount--
 
@@ -173,7 +185,11 @@ export function transformStreamWithRouter(
     .then(() => {
       clearTimeout(timeoutHandle)
       const finalHtml =
-        leftoverHtml + getBufferedRouterStream() + pendingClosingTags
+        leftover + leftoverHtml + getBufferedRouterStream() + pendingClosingTags
+
+      leftover = ''
+      leftoverHtml = ''
+      pendingClosingTags = ''
 
       finalPassThrough.end(finalHtml)
     })
@@ -217,15 +233,20 @@ export function transformStreamWithRouter(
         pendingClosingTags = chunkString.slice(bodyEndIndex)
 
         finalPassThrough.write(
-          chunkString.slice(0, bodyEndIndex) + getBufferedRouterStream(),
+          chunkString.slice(0, bodyEndIndex) +
+            getBufferedRouterStream() +
+            leftoverHtml,
         )
 
         leftover = ''
+        leftoverHtml = ''
         return
       }
 
       let result: RegExpExecArray | null
       let lastIndex = 0
+      // Reset regex lastIndex since it's global and stateful across exec() calls
+      patternClosingTag.lastIndex = 0
       while ((result = patternClosingTag.exec(chunkString)) !== null) {
         lastIndex = result.index + result[0].length
       }
@@ -238,12 +259,18 @@ export function transformStreamWithRouter(
 
         finalPassThrough.write(processed)
         leftover = chunkString.slice(lastIndex)
+        leftoverHtml = ''
       } else {
         leftover = chunkString
         leftoverHtml += getBufferedRouterStream()
       }
     },
     onEnd: () => {
+      // Don't process if stream was already destroyed/cancelled
+      if (finalPassThrough.destroyed) {
+        return
+      }
+
       // Mark the app as done rendering
       isAppRendering = false
       router.serverSsr!.setRenderFinished()
@@ -262,6 +289,15 @@ export function transformStreamWithRouter(
     },
     onError: (error) => {
       console.error('Error reading appStream:', error)
+      isAppRendering = false
+      router.serverSsr!.setRenderFinished()
+      // Clear timeout to prevent it from firing after error
+      clearTimeout(timeoutHandle)
+      // Clear string buffers to prevent memory leaks
+      leftover = ''
+      leftoverHtml = ''
+      routerStreamBuffer = ''
+      pendingClosingTags = ''
       finalPassThrough.destroy(error)
       injectedHtmlDonePromise.reject(error)
     },