diff --git a/synapse/storage/databases/main/events_bg_updates.py b/synapse/storage/databases/main/events_bg_updates.py
index b56325a4a2..2be7c6df3b 100644
--- a/synapse/storage/databases/main/events_bg_updates.py
+++ b/synapse/storage/databases/main/events_bg_updates.py
@@ -1664,7 +1664,11 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
                                 _BackgroundUpdates.SLIDING_SYNC_JOINED_ROOMS_BACKFILL,
                                 {"last_room_id": room_id},
                             )
-                        # Raising exception so we can just exit and try again
+                        # Raising exception so we can just exit and try again. It would
+                        # be hard to resolve this within the transaction because we need
+                        # to get full events out that take redactions into account. We
+                        # could add some retry logic here, but it's easier to just let
+                        # the background update try again.
                         raise Exception(
                             "Current state was updated after we gathered it to update "
                             + "`sliding_sync_joined_rooms` in the background update. "
@@ -1676,8 +1680,13 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
                 insert_keys = insert_map.keys()
                 insert_values = insert_map.values()
                 # Since we partially update the `sliding_sync_joined_rooms` as new state
-                # is sent, we need to update the fields `ON CONFLICT`. We just have to be careful
-                # we're not overwriting it with stale data.
+                # is sent, we need to update the state fields `ON CONFLICT`. We just
+                # have to be careful we're not overwriting it with stale data (see
+                # `last_current_state_delta_stream_id` check above).
+                #
+                # We don't need to update `event_stream_ordering` and `bump_stamp` `ON
+                # CONFLICT` because if they are present, that means they are already
+                # up-to-date.
                 sql = f"""
                     INSERT INTO sliding_sync_joined_rooms
                         (room_id, event_stream_ordering, bump_stamp, {", ".join(insert_keys)})
@@ -1687,16 +1696,6 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
                     )
                     ON CONFLICT (room_id)
                     DO UPDATE SET
-                        event_stream_ordering = CASE
-                            WHEN event_stream_ordering IS NULL OR event_stream_ordering < EXCLUDED.event_stream_ordering
-                                THEN EXCLUDED.event_stream_ordering
-                            ELSE event_stream_ordering
-                        END,
-                        bump_stamp = CASE
-                            WHEN bump_stamp IS NULL OR bump_stamp < EXCLUDED.bump_stamp
-                                THEN EXCLUDED.bump_stamp
-                            ELSE bump_stamp
-                        END,
                         {", ".join(f"{key} = EXCLUDED.{key}" for key in insert_keys)}
                     """
                 args = [room_id, event_stream_ordering, bump_stamp] + list(