diff --git a/application/src/main/java/run/halo/app/core/attachment/ThumbnailGenerator.java b/application/src/main/java/run/halo/app/core/attachment/ThumbnailGenerator.java
index 59f543e75..ad822f05c 100644
--- a/application/src/main/java/run/halo/app/core/attachment/ThumbnailGenerator.java
+++ b/application/src/main/java/run/halo/app/core/attachment/ThumbnailGenerator.java
@@ -6,6 +6,7 @@ import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
 import java.net.URISyntaxException;
 import java.net.URL;
@@ -172,7 +173,11 @@ public class ThumbnailGenerator {
             File tempFile = File.createTempFile("halo-image-thumb-", ".tmp");
             long totalBytesDownloaded = 0;
             var tempFilePath = tempFile.toPath();
-            try (InputStream inputStream = url.openStream();
+            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
+            connection.setRequestProperty("User-Agent",
+                "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko)"
+                    + " Chrome/92.0.4515.131 Safari/537.36");
+            try (InputStream inputStream = connection.getInputStream();
                  FileOutputStream outputStream = new FileOutputStream(tempFile)) {
 
                 byte[] buffer = new byte[4096];
diff --git a/application/src/main/java/run/halo/app/core/attachment/reconciler/AttachmentReconciler.java b/application/src/main/java/run/halo/app/core/attachment/reconciler/AttachmentReconciler.java
index 0441390cc..fa5b722ba 100644
--- a/application/src/main/java/run/halo/app/core/attachment/reconciler/AttachmentReconciler.java
+++ b/application/src/main/java/run/halo/app/core/attachment/reconciler/AttachmentReconciler.java
@@ -58,7 +58,7 @@ public class AttachmentReconciler implements Reconciler<Request> {
             var annotations = attachment.getMetadata().getAnnotations();
             if (annotations != null) {
                 attachmentService.getPermalink(attachment)
-                    .map(URI::toString)
+                    .map(URI::toASCIIString)
                     .switchIfEmpty(Mono.fromSupplier(() -> {
                         // Only for back-compatibility
                         return annotations.get(Constant.EXTERNAL_LINK_ANNO_KEY);
diff --git a/application/src/main/java/run/halo/app/core/attachment/reconciler/LocalThumbnailsReconciler.java b/application/src/main/java/run/halo/app/core/attachment/reconciler/LocalThumbnailsReconciler.java
index 1f1eb7b38..ce2d90f82 100644
--- a/application/src/main/java/run/halo/app/core/attachment/reconciler/LocalThumbnailsReconciler.java
+++ b/application/src/main/java/run/halo/app/core/attachment/reconciler/LocalThumbnailsReconciler.java
@@ -27,6 +27,7 @@ import run.halo.app.core.extension.attachment.Attachment;
 import run.halo.app.core.extension.attachment.Constant;
 import run.halo.app.core.extension.attachment.LocalThumbnail;
 import run.halo.app.extension.ExtensionClient;
+import run.halo.app.extension.ExtensionUtil;
 import run.halo.app.extension.ListOptions;
 import run.halo.app.extension.PageRequestImpl;
 import run.halo.app.extension.controller.Controller;
@@ -47,6 +48,9 @@ public class LocalThumbnailsReconciler implements Reconciler<Reconciler.Request>
     public Result reconcile(Request request) {
         client.fetch(LocalThumbnail.class, request.name())
             .ifPresent(thumbnail -> {
+                if (ExtensionUtil.isDeleted(thumbnail)) {
+                    return;
+                }
                 if (shouldGenerate(thumbnail)) {
                     requestGenerateThumbnail(thumbnail);
                     nullSafeAnnotations(thumbnail).remove(REQUEST_TO_GENERATE_ANNO);
diff --git a/application/src/test/java/run/halo/app/core/attachment/ThumbnailGeneratorTest.java b/application/src/test/java/run/halo/app/core/attachment/ThumbnailGeneratorTest.java
index e50da39ba..a87dca886 100644
--- a/application/src/test/java/run/halo/app/core/attachment/ThumbnailGeneratorTest.java
+++ b/application/src/test/java/run/halo/app/core/attachment/ThumbnailGeneratorTest.java
@@ -4,11 +4,13 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.HttpURLConnection;
 import java.net.URL;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -57,7 +59,9 @@ class ThumbnailGeneratorTest {
             String mockImageData = "fakeImageData";
             InputStream mockInputStream = new ByteArrayInputStream(mockImageData.getBytes());
 
-            doAnswer(invocation -> mockInputStream).when(spyImageUrl).openStream();
+            var urlConnection = mock(HttpURLConnection.class);
+            doAnswer(invocation -> urlConnection).when(spyImageUrl).openConnection();
+            doReturn(mockInputStream).when(urlConnection).getInputStream();
 
             var path = imageDownloader.downloadFileInternal(spyImageUrl);
             assertThat(path).isNotNull();
@@ -81,8 +85,9 @@ class ThumbnailGeneratorTest {
             var fileSizeByte = ThumbnailGenerator.MAX_FILE_SIZE + 10;
             byte[] largeImageData = new byte[fileSizeByte];
             InputStream mockInputStream = new ByteArrayInputStream(largeImageData);
-
-            doReturn(mockInputStream).when(spyImageUrl).openStream();
+            var urlConnection = mock(HttpURLConnection.class);
+            doAnswer(invocation -> urlConnection).when(spyImageUrl).openConnection();
+            doReturn(mockInputStream).when(urlConnection).getInputStream();
             assertThatThrownBy(() -> imageDownloader.downloadFileInternal(spyImageUrl))
                 .isInstanceOf(IOException.class)
                 .hasMessageContaining("File size exceeds the limit");