diff --git a/crates/loro-core/src/fuzz/recursive.rs b/crates/loro-core/src/fuzz/recursive.rs
index 38172f78..55f188d0 100644
--- a/crates/loro-core/src/fuzz/recursive.rs
+++ b/crates/loro-core/src/fuzz/recursive.rs
@@ -909,6 +909,40 @@ mod failed_tests {
         )
     }
 
+    #[test]
+    fn unknown() {
+        test_multi_sites(
+            5,
+            &mut [
+                Map {
+                    site: 0,
+                    container_idx: 0,
+                    key: 0,
+                    value: Container(C::Map),
+                },
+                SyncAll,
+                Map {
+                    site: 0,
+                    container_idx: 0,
+                    key: 0,
+                    value: Container(C::List),
+                },
+                Map {
+                    site: 1,
+                    container_idx: 1,
+                    key: 255,
+                    value: Container(C::List),
+                },
+                Map {
+                    site: 4,
+                    container_idx: 1,
+                    key: 9,
+                    value: Null,
+                },
+            ],
+        )
+    }
+
     #[test]
     fn path_issue() {
         test_multi_sites(
diff --git a/crates/loro-core/src/hierarchy.rs b/crates/loro-core/src/hierarchy.rs
index c0ea042d..73e79f73 100644
--- a/crates/loro-core/src/hierarchy.rs
+++ b/crates/loro-core/src/hierarchy.rs
@@ -128,13 +128,13 @@ impl Hierarchy {
         reg: &ContainerRegistry,
         descendant: &ContainerID,
         target: Option<&ContainerID>,
-    ) -> Path {
+    ) -> Option<Path> {
         if let ContainerID::Root { name, .. } = descendant {
-            return vec![Index::Key(name.into())];
+            return Some(vec![Index::Key(name.into())]);
         }
 
         if target.map(|x| x == descendant).unwrap_or(false) {
-            return vec![];
+            return Some(vec![]);
         }
 
         let mut path = Path::default();
@@ -155,7 +155,7 @@ impl Hierarchy {
                         name,
                         container_type: _,
                     } => path.push(Index::Key(name.clone())),
-                    _ => unreachable!(),
+                    _ => return None,
                 }
             }
 
@@ -167,7 +167,7 @@ impl Hierarchy {
         }
 
         path.reverse();
-        path
+        Some(path)
     }
 
     pub fn should_notify(&self, container_id: &ContainerID) -> bool {
@@ -211,7 +211,7 @@ impl Hierarchy {
         // otherwise, the paths to children may be incorrect when the parents are affected by some of the events
         let mut event_and_paths = raw_events
             .into_iter()
-            .map(|x| (self.get_path(reg, &x.container_id, None), x))
+            .filter_map(|x| self.get_path(reg, &x.container_id, None).map(|y| (y, x)))
             .collect::<Vec<_>>();
         event_and_paths.sort_by_cached_key(|x| x.0.len());
         for (path, event) in event_and_paths {
@@ -220,7 +220,9 @@ impl Hierarchy {
     }
 
     pub fn notify(&mut self, raw_event: RawEvent, reg: &ContainerRegistry) {
-        let absolute_path = self.get_path(reg, &raw_event.container_id, None);
+        let Some(absolute_path) = self.get_path(reg, &raw_event.container_id, None) else {
+            return;
+        };
         self.notify_with_path(raw_event, absolute_path);
     }
 
diff --git a/deno.jsonc b/deno.jsonc
index ba83326e..578ca056 100644
--- a/deno.jsonc
+++ b/deno.jsonc
@@ -1,6 +1,8 @@
 {
   "tasks": {
     "build": "cargo build",
+    // to debug a single test use
+    // UST_BACKTRACE=full DEBUG=* cargo test --package loro-core --lib --features test_utils --features wasm -- fuzz::recursive::failed_tests::unknown --exact --nocapture &> debug.log
     "test": "RUST_BACKTRACE=full cargo nextest run --features=test_utils",
     "test-all": "deno task test & deno task quick-fuzz & deno task test-wasm",
     "test-prop": "RUSTFLAGS='--cfg=proptest' cargo nextest run --features=test_utils",