diff -ur Trac-1.4.3.orig/trac/notification/api.py Trac-1.4.3/trac/notification/api.py
--- Trac-1.4.3.orig/trac/notification/api.py	2021-05-10 07:14:13.000000000 +0900
+++ Trac-1.4.3/trac/notification/api.py	2023-01-16 18:26:51.804001854 +0900
@@ -23,6 +23,7 @@
                          ListOption, Option)
 from trac.core import Component, Interface, ExtensionPoint
 from trac.util import as_bool, lazy, to_list
+from trac.util.text import exception_to_unicode
 
 
 __all__ = ['IEmailAddressResolver', 'IEmailDecorator', 'IEmailSender',
@@ -209,6 +210,11 @@
         self.time = time
         self.author = author
 
+    def __repr__(self):
+        return '<%s realm=%r, category=%r, target=%r, time=%r, author=%r>' % \
+               (self.__class__.__name__, self.realm, self.category,
+                self.target, self.time, self.author)
+
 
 class NotificationSystem(Component):
 
@@ -370,7 +376,12 @@
 
         :param event: a `NotificationEvent`
         """
-        self.distribute_event(event, self.subscriptions(event))
+        try:
+            self.distribute_event(event, self.subscriptions(event))
+        except Exception as e:
+            self.log.error("Failure distributing event %r%s", event,
+                           exception_to_unicode(e, traceback=True))
+            raise
 
     def distribute_event(self, event, subscriptions):
         """Distribute a event to all subscriptions.
diff -ur Trac-1.4.3.orig/trac/ticket/notification.py Trac-1.4.3/trac/ticket/notification.py
--- Trac-1.4.3.orig/trac/ticket/notification.py	2021-05-10 07:14:13.000000000 +0900
+++ Trac-1.4.3/trac/ticket/notification.py	2023-01-16 18:26:59.340082792 +0900
@@ -690,6 +690,14 @@
             # Harvest previous CC field
             if 'fields' in event.changes and 'cc' in event.changes['fields']:
                 cc_users.update(to_set(event.changes['fields']['cc']['old']))
+
+            # Get members of permission groups
+            groups = PermissionSystem(self.env).get_groups_dict()
+            for cc in sorted(cc_users):
+                if cc in groups:
+                    cc_users.discard(cc)
+                    cc_users.update(groups[cc])
+
         return _ticket_change_subscribers(self, cc_users)
 
     def description(self):
@@ -751,13 +759,6 @@
     if not isinstance(candidates, (list, set, tuple)):
         candidates = [candidates]
 
-    # Get members of permission groups
-    groups = PermissionSystem(subscriber.env).get_groups_dict()
-    for cc in set(candidates):
-        if cc in groups:
-            candidates.remove(cc)
-            candidates.update(groups[cc])
-
     matcher = RecipientMatcher(subscriber.env)
     klass = subscriber.__class__.__name__
     sids = set()