diff --git a/lib/utils/delete-message-utils.js b/lib/utils/delete-message-utils.js
--- a/lib/utils/delete-message-utils.js
+++ b/lib/utils/delete-message-utils.js
@@ -21,7 +21,10 @@
 import { isComposableMessageType } from '../types/message-types.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
-import { thickThreadTypes } from '../types/thread-types-enum.js';
+import {
+  thickThreadTypes,
+  threadTypeIsThick,
+} from '../types/thread-types-enum.js';
 
 const deletedMessageText = 'Deleted message';
 
@@ -110,6 +113,16 @@
     return true;
   }
 
+  if (
+    threadTypeIsThick(threadInfo.type) &&
+    targetMessageInfo.time < threadInfo.creationTime
+  ) {
+    // This code blocks deleting a sidebar source in thick threads - we
+    // don't handle it correctly now. We have a task to track
+    // https://linear.app/comm/issue/ENG-10528/handle-message-edit-and-delete-of-a-sidebar-source-in-thick-threads
+    return false;
+  }
+
   return (
     currentUserInfo.id === targetMessageInfo.creator.id && canDeleteOwnMessages
   );
diff --git a/web/tooltips/tooltip-action-utils.js b/web/tooltips/tooltip-action-utils.js
--- a/web/tooltips/tooltip-action-utils.js
+++ b/web/tooltips/tooltip-action-utils.js
@@ -427,18 +427,12 @@
   const togglePinAction = useMessageTogglePinAction(item, threadInfo);
   const editAction = useMessageEditAction(item, threadInfo);
   const deleteAction = useMessageDeleteAction(item, threadInfo);
-  return React.useMemo(
-    () =>
-      [
-        replyAction,
-        sidebarAction,
-        copyAction,
-        reactAction,
-        togglePinAction,
-        editAction,
-        deleteAction,
-      ].filter(Boolean),
-    [
+
+  return React.useMemo(() => {
+    if (item.deleted) {
+      return [];
+    }
+    return [
       replyAction,
       sidebarAction,
       copyAction,
@@ -446,8 +440,17 @@
       togglePinAction,
       editAction,
       deleteAction,
-    ],
-  );
+    ].filter(Boolean);
+  }, [
+    item.deleted,
+    replyAction,
+    sidebarAction,
+    copyAction,
+    reactAction,
+    togglePinAction,
+    editAction,
+    deleteAction,
+  ]);
 }
 
 const undefinedTooltipSize = {