Queries waiting on SyncRep even though synchronous_standby_names is absent

Hi Team,

PostgreSQL : 13.6

I saw a strange behavior today. All write queries were stuck on the
'SyncRep' wait event so I reset the synchronous_standby_names.

postgres=# show synchronous_standby_names ;
> synchronous_standby_names
> ---------------------------
>
> (1 row)

We still saw many queries waiting on SyncRep

datid | datname | pid | leader_pid | usesysid | usename |
> application_name | client_addr | client_hostname | client_port | backend_start
> | xact_start | query_start
> | state_change | wait_event_type | wait_event |
> state | backend_xid | backend_xmin |
> query | backend_type
>
> -------+----------+-------+------------+----------+---------+------------------+-------------+-----------------+-------------+-------------------------------+-------------------------------+------------------------
>
> -------+-------------------------------+-----------------+------------+--------+-------------+--------------+-------------------------------------------------------------------------------------+----------------
> 16401 | repmgr | 24344 | | 16385 | postgres | psql
> | | | -1 | 2024-07-14
> 09:55:09.615682+00 | 2024-07-14 09:55:09.622254+00 | 2024-07-14 09:55:09.622
> 254+00 | 2024-07-14 09:55:09.622255+00 | IPC | SyncRep |
> active | 343975184 | 343974710 | UPDATE repmgr.sync_check SET
> row_update_time = (select timezone('UTC', now())) | client backend
> (1 row)

Has anyone faced this issue or have any inputs

Thank you,

Nikhil