diff --git a/rmw_zenoh_cpp/src/detail/event.hpp b/rmw_zenoh_cpp/src/detail/event.hpp
index 8691c3ce..ca18ca30 100644
--- a/rmw_zenoh_cpp/src/detail/event.hpp
+++ b/rmw_zenoh_cpp/src/detail/event.hpp
@@ -158,12 +158,7 @@ class EventsManager
   mutable std::mutex event_condition_mutex_;
   /// Condition variable to attach for event notifications.
   std::condition_variable * event_conditions_[ZENOH_EVENT_ID_MAX + 1]{nullptr};
-  /// User callback that can be set via data_callback_mgr.set_callback().
-  rmw_event_callback_t callback_ {nullptr};
-  /// User data that should be passed to the user callback.
-  const void * user_data_ {nullptr};
-  /// Count for
-  size_t unread_count_ {0};
+
   rmw_event_callback_t event_callback_[ZENOH_EVENT_ID_MAX + 1] {nullptr};
   const void * event_data_[ZENOH_EVENT_ID_MAX + 1] {nullptr};
   size_t event_unread_count_[ZENOH_EVENT_ID_MAX + 1] {0};
diff --git a/rmw_zenoh_cpp/src/detail/liveliness_utils.cpp b/rmw_zenoh_cpp/src/detail/liveliness_utils.cpp
index dce43cd5..78d5b412 100644
--- a/rmw_zenoh_cpp/src/detail/liveliness_utils.cpp
+++ b/rmw_zenoh_cpp/src/detail/liveliness_utils.cpp
@@ -88,7 +88,6 @@ static const char PUB_STR[] = "MP";
 static const char SUB_STR[] = "MS";
 static const char SRV_STR[] = "SS";
 static const char CLI_STR[] = "SC";
-static const char EMPTY_NAMESPACE_REPLACEMENT = '_';
 static const char KEYEXPR_DELIMITER = '/';
 static const char SLASH_REPLACEMENT = '%';
 static const char QOS_DELIMITER = ':';
@@ -261,7 +260,7 @@ Entity::Entity(
   keyexpr_parts[KeyexprIndex::Id] = id_;
   keyexpr_parts[KeyexprIndex::EntityStr] = entity_to_str.at(type_);
   // An empty namespace from rcl will contain "/" but zenoh does not allow keys with "//".
-  // Hence we add an "_" to denote an empty namespace such that splitting the key
+  // Hence we mangle the empty namespace such that splitting the key
   // will always result in 5 parts.
   keyexpr_parts[KeyexprIndex::Namespace] = mangle_name(node_info_.ns_);
   keyexpr_parts[KeyexprIndex::NodeName] = mangle_name(node_info_.name_);
diff --git a/rmw_zenoh_cpp/src/detail/rmw_data_types.cpp b/rmw_zenoh_cpp/src/detail/rmw_data_types.cpp
index 895124b3..446fe13f 100644
--- a/rmw_zenoh_cpp/src/detail/rmw_data_types.cpp
+++ b/rmw_zenoh_cpp/src/detail/rmw_data_types.cpp
@@ -31,6 +31,24 @@
 #include "attachment_helpers.hpp"
 #include "rmw_data_types.hpp"
 
+///=============================================================================
+static size_t hash_gid(const uint8_t * gid)
+{
+  std::stringstream hash_str;
+  hash_str << std::hex;
+  size_t i = 0;
+  for (; i < (RMW_GID_STORAGE_SIZE - 1); i++) {
+    hash_str << static_cast<int>(gid[i]);
+  }
+  return std::hash<std::string>{}(hash_str.str());
+}
+
+///=============================================================================
+static size_t hash_gid(const rmw_request_id_t & request_id)
+{
+  return hash_gid(request_id.writer_guid);
+}
+
 ///=============================================================================
 size_t rmw_context_impl_s::get_next_entity_id()
 {
@@ -135,7 +153,24 @@ void rmw_subscription_data_t::add_new_message(
     }
   }
 
-  // TODO(Yadunund): Check for ZENOH_EVENT_MESSAGE_LOST.
+  // Check for messages lost if the new sequence number is not monotonically increasing.
+  const size_t gid_hash = hash_gid(msg->publisher_gid);
+  auto last_known_pub_it = last_known_published_msg_.find(gid_hash);
+  if (last_known_pub_it != last_known_published_msg_.end()) {
+    const int64_t seq_increment = std::abs(msg->sequence_number - last_known_pub_it->second);
+    if (seq_increment > 1) {
+      const size_t num_msg_lost = seq_increment - 1;
+      total_messages_lost_ += num_msg_lost;
+      auto event_status = std::make_unique<rmw_zenoh_event_status_t>();
+      event_status->total_count_change = num_msg_lost;
+      event_status->total_count = total_messages_lost_;
+      events_mgr.add_new_event(
+        rmw_zenoh_cpp::ZENOH_EVENT_MESSAGE_LOST,
+        std::move(event_status));
+    }
+  }
+  // Always update the last known sequence number for the publisher
+  last_known_published_msg_[gid_hash] = msg->sequence_number;
 
   message_queue_.emplace_back(std::move(msg));
 
@@ -211,17 +246,6 @@ void rmw_service_data_t::add_new_query(std::unique_ptr<ZenohQuery> query)
   notify();
 }
 
-static size_t hash_gid(const rmw_request_id_t & request_id)
-{
-  std::stringstream hash_str;
-  hash_str << std::hex;
-  size_t i = 0;
-  for (; i < (RMW_GID_STORAGE_SIZE - 1); i++) {
-    hash_str << static_cast<int>(request_id.writer_guid[i]);
-  }
-  return std::hash<std::string>{}(hash_str.str());
-}
-
 ///=============================================================================
 bool rmw_service_data_t::add_to_query_map(
   const rmw_request_id_t & request_id, std::unique_ptr<ZenohQuery> query)
diff --git a/rmw_zenoh_cpp/src/detail/rmw_data_types.hpp b/rmw_zenoh_cpp/src/detail/rmw_data_types.hpp
index 285c00a9..a43af5d3 100644
--- a/rmw_zenoh_cpp/src/detail/rmw_data_types.hpp
+++ b/rmw_zenoh_cpp/src/detail/rmw_data_types.hpp
@@ -191,6 +191,10 @@ class rmw_subscription_data_t final
   std::deque<std::unique_ptr<saved_msg_data>> message_queue_;
   mutable std::mutex message_queue_mutex_;
 
+  // Map GID of a publisher to the sequence number of the message it published.
+  std::unordered_map<size_t, int64_t> last_known_published_msg_;
+  size_t total_messages_lost_{0};
+
   void notify();
 
   std::condition_variable * condition_{nullptr};