diff --git a/changelog.d/7482.bugfix b/changelog.d/7482.bugfix
new file mode 100644
index 000000000..018bf5cc8
--- /dev/null
+++ b/changelog.d/7482.bugfix
@@ -0,0 +1 @@
+Fix Redis reconnection logic that can result in missed updates over replication if master reconnects to Redis without restarting.
diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index 1b0546848..e6a50aa74 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -151,6 +151,13 @@ class ReplicationCommandHandler:
             hs.get_reactor().connectTCP(host, port, self._factory)
 
     async def on_REPLICATE(self, conn: AbstractConnection, cmd: ReplicateCommand):
+        self.send_positions_to_connection(conn)
+
+    def send_positions_to_connection(self, conn: AbstractConnection):
+        """Send current position of all streams this process is source of to
+        the connection.
+        """
+
         # We only want to announce positions by the writer of the streams.
         # Currently this is just the master process.
         if not self._is_master:
@@ -158,7 +165,7 @@ class ReplicationCommandHandler:
 
         for stream_name, stream in self._streams.items():
             current_token = stream.current_token(self._instance_name)
-            self.send_command(
+            conn.send_command(
                 PositionCommand(stream_name, self._instance_name, current_token)
             )
 
diff --git a/synapse/replication/tcp/redis.py b/synapse/replication/tcp/redis.py
index 55bfa71df..e776b6318 100644
--- a/synapse/replication/tcp/redis.py
+++ b/synapse/replication/tcp/redis.py
@@ -70,7 +70,6 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
         logger.info("Connected to redis")
         super().connectionMade()
         run_as_background_process("subscribe-replication", self._send_subscribe)
-        self.handler.new_connection(self)
 
     async def _send_subscribe(self):
         # it's important to make sure that we only send the REPLICATE command once we
@@ -81,9 +80,15 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
         logger.info(
             "Successfully subscribed to redis stream, sending REPLICATE command"
         )
+        self.handler.new_connection(self)
         await self._async_send_command(ReplicateCommand())
         logger.info("REPLICATE successfully sent")
 
+        # We send out our positions when there is a new connection in case the
+        # other side missed updates. We do this for Redis connections as the
+        # otherside won't know we've connected and so won't issue a REPLICATE.
+        self.handler.send_positions_to_connection(self)
+
     def messageReceived(self, pattern: str, channel: str, message: str):
         """Received a message from redis.
         """