diff --git a/lib/KOReaderSync/KOReaderSyncClient.cpp b/lib/KOReaderSync/KOReaderSyncClient.cpp
index 123d449b..7253416f 100644
--- a/lib/KOReaderSync/KOReaderSyncClient.cpp
+++ b/lib/KOReaderSync/KOReaderSyncClient.cpp
@@ -86,7 +86,17 @@ ResponseBuffer g_sessionResponseBuf;
 void clearResponseBuffer(ResponseBuffer* buf) {
   if (!buf) return;
   if (buf->data) {
-    buf->len = 0;
+    free(buf->data);
+    buf->data = nullptr;
+  }
+  buf->len = 0;
+  buf->capacity = 0;
+}
+
+void resetResponseBuffer(ResponseBuffer* buf) {
+  if (!buf) return;
+  buf->len = 0;
+  if (buf->data) {
     buf->data[0] = '\0';
   }
 }
@@ -272,7 +282,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::registerUser() {
 
   ResponseBuffer buf;
   ResponseBuffer* activeBuf = effectiveResponseBuffer(&buf);
-  clearResponseBuffer(activeBuf);
+  resetResponseBuffer(activeBuf);
   esp_http_client_handle_t client = createClient(url.c_str(), &buf, HTTP_METHOD_POST);
   if (!client) {
     lastEspError = ESP_ERR_NO_MEM;
@@ -334,7 +344,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::authenticate() {
 
   ResponseBuffer buf;
   ResponseBuffer* activeBuf = effectiveResponseBuffer(&buf);
-  clearResponseBuffer(activeBuf);
+  resetResponseBuffer(activeBuf);
   esp_http_client_handle_t client = createClient(url.c_str(), &buf);
   if (!client) {
     lastEspError = ESP_ERR_NO_MEM;
@@ -385,7 +395,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::getProgress(const std::string& doc
       return NETWORK_ERROR;
     }
 
-    clearResponseBuffer(activeBuf);
+    resetResponseBuffer(activeBuf);
 
     esp_http_client_handle_t client = createClient(url.c_str(), &buf);
     if (!client) {
@@ -487,7 +497,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::updateProgress(const KOReaderProgr
       return NETWORK_ERROR;
     }
 
-    clearResponseBuffer(activeBuf);
+    resetResponseBuffer(activeBuf);
 
     esp_http_client_handle_t client = createClient(url.c_str(), &buf, HTTP_METHOD_PUT);
     if (!client) {
diff --git a/src/activities/reader/KOReaderSyncActivity.cpp b/src/activities/reader/KOReaderSyncActivity.cpp
index 3cb1343b..b63582c4 100644
--- a/src/activities/reader/KOReaderSyncActivity.cpp
+++ b/src/activities/reader/KOReaderSyncActivity.cpp
@@ -127,7 +127,15 @@ void KOReaderSyncActivity::performSync() {
       statusMessage = tr(STR_MAPPING_LOCAL);
     }
     requestUpdateAndWait();
-    computeLocalProgressAndChapter();
+    if (!computeLocalProgressAndChapter()) {
+      {
+        RenderLock lock(*this);
+        state = SYNC_FAILED;
+        statusMessage = tr(STR_SYNC_FAILED_MSG);
+      }
+      requestUpdate(true);
+      return;
+    }
   }
 
   // Drop EPUB state before HTTPS to maximize contiguous heap for TLS.
@@ -221,19 +229,14 @@ void KOReaderSyncActivity::performSync() {
   // Defer remote EPUB mapping until user chooses Apply. Upload only needs the
   // precomputed local XPath, so this avoids post-fetch inflate churn and keeps
   // the GET session reusable for PUT.
-  hasRemoteProgress = true;
+  hasRemoteProgress = false;
   remotePositionMapped = false;
-  remotePosition.spineIndex = currentSpineIndex;
-  remotePosition.pageNumber = 0;
+  remotePosition.spineIndex = -1;
+  remotePosition.pageNumber = -1;
   remotePosition.totalPages = 0;
   remotePosition.paragraphIndex = 0;
   remotePosition.hasParagraphIndex = false;
-  int xpathSpineIndex = -1;
-  if (ChapterXPathIndexer::tryExtractSpineIndexFromXPath(remoteProgress.progress, xpathSpineIndex) &&
-      xpathSpineIndex >= 0) {
-    remotePosition.spineIndex = xpathSpineIndex;
-  }
-  remoteChapterLabel = tr(STR_UNNAMED);
+  remoteChapterLabel.clear();
 
   if (syncIntent == SyncIntent::PULL_REMOTE) {
     // Pull intent applies immediately and exits. We bypass chooser UI to keep
@@ -291,7 +294,15 @@ void KOReaderSyncActivity::performUpload() {
   // If sync reached this screen without cached local progress, compute it now.
   // This keeps upload robust when UI flow changes or retries happen.
   if (localProgress.xpath.empty()) {
-    computeLocalProgressAndChapter();
+    if (!computeLocalProgressAndChapter()) {
+      {
+        RenderLock lock(*this);
+        state = SYNC_FAILED;
+        statusMessage = tr(STR_SYNC_FAILED_MSG);
+      }
+      requestUpdate(true);
+      return;
+    }
     releaseEpubForMapping();
   }
 
@@ -431,13 +442,15 @@ void KOReaderSyncActivity::render(RenderLock&&) {
 
     // Remote progress - chapter and page
     renderer.drawText(UI_10_FONT_ID, contentRect.x + 20, 160, tr(STR_REMOTE_LABEL), true);
-    char remoteChapterStr[128];
-    snprintf(remoteChapterStr, sizeof(remoteChapterStr), "  %s", remoteChapter.c_str());
-    renderer.drawText(UI_10_FONT_ID, contentRect.x + 20, 185, remoteChapterStr);
-    char remotePageStr[64];
-    snprintf(remotePageStr, sizeof(remotePageStr), tr(STR_PAGE_OVERALL_FORMAT), remotePosition.pageNumber + 1,
-             remoteProgress.percentage * 100);
-    renderer.drawText(UI_10_FONT_ID, contentRect.x + 20, 210, remotePageStr);
+    if (hasRemoteProgress) {
+      char remoteChapterStr[128];
+      snprintf(remoteChapterStr, sizeof(remoteChapterStr), "  %s", remoteChapter.c_str());
+      renderer.drawText(UI_10_FONT_ID, contentRect.x + 20, 185, remoteChapterStr);
+      char remotePageStr[64];
+      snprintf(remotePageStr, sizeof(remotePageStr), tr(STR_PAGE_OVERALL_FORMAT), remotePosition.pageNumber + 1,
+               remoteProgress.percentage * 100);
+      renderer.drawText(UI_10_FONT_ID, contentRect.x + 20, 210, remotePageStr);
+    }
 
     if (!remoteProgress.device.empty()) {
       char deviceStr[64];
@@ -556,15 +569,18 @@ bool KOReaderSyncActivity::ensureRemotePositionMapped() {
   remotePosition = ProgressMapper::toCrossPoint(epub, koPos, currentSpineIndex, totalPagesInSpine);
   computeRemoteChapter();
   releaseEpubForMapping();
+  hasRemoteProgress = true;
   remotePositionMapped = true;
   return true;
 }
 
 void KOReaderSyncActivity::releaseEpubForMapping() { epub.reset(); }
 
-void KOReaderSyncActivity::computeLocalProgressAndChapter() {
+bool KOReaderSyncActivity::computeLocalProgressAndChapter() {
   if (!ensureEpubLoadedForMapping()) {
-    return;
+    localProgress = KOReaderPosition{};
+    localChapterLabel.clear();
+    return false;
   }
 
   CrossPointPosition localPos = {currentSpineIndex, currentPage, totalPagesInSpine, localParagraphIndex,
@@ -575,6 +591,7 @@ void KOReaderSyncActivity::computeLocalProgressAndChapter() {
   localChapterLabel = (localTocIndex >= 0)
                           ? epub->getTocItem(localTocIndex).title
                           : (std::string(tr(STR_SECTION_PREFIX)) + std::to_string(currentSpineIndex + 1));
+  return true;
 }
 
 void KOReaderSyncActivity::computeRemoteChapter() {
diff --git a/src/activities/reader/KOReaderSyncActivity.h b/src/activities/reader/KOReaderSyncActivity.h
index 25b87599..0389276a 100644
--- a/src/activities/reader/KOReaderSyncActivity.h
+++ b/src/activities/reader/KOReaderSyncActivity.h
@@ -113,7 +113,7 @@ class KOReaderSyncActivity final : public Activity {
   void closeCancelled();
   bool ensureEpubLoadedForMapping();
   void releaseEpubForMapping();
-  void computeLocalProgressAndChapter();
+  bool computeLocalProgressAndChapter();
   void computeRemoteChapter();
   bool ensureRemotePositionMapped();
 };