system catalog performance

Under what circumstances would the following query be extra slow?

SELECT
  pg_catalog.to_char(pg_catalog.pg_postmaster_start_time(), 'YYYY-MM-DD HH24:MI:SS.MS TZ'),
  CASE WHEN pg_catalog.pg_is_in_recovery() THEN 0 ELSE ('x' ||
pg_catalog.substr(pg_catalog.pg_walfile_name(pg_catalog.pg_current_wal_lsn()),1, 8))::bit(32)::int END,  
  CASE WHEN pg_catalog.pg_is_in_recovery() THEN 0 ELSE pg_catalog.pg_wal_lsn_diff(pg_catalog.pg_current_wal_lsn(),
'0/0')::bigintEND,  
  pg_catalog.pg_wal_lsn_diff(pg_catalog.pg_last_wal_replay_lsn(), '0/0')::bigint,
  pg_catalog.pg_wal_lsn_diff(COALESCE(pg_catalog.pg_last_wal_receive_lsn(), '0/0'), '0/0')::bigint,
  pg_catalog.pg_is_in_recovery() AND pg_catalog.pg_is_wal_replay_paused(),
  pg_catalog.to_char(pg_catalog.pg_last_xact_replay_timestamp(), 'YYYY-MM-DD HH24:MI:SS.MS TZ'),
  pg_catalog.array_to_json(pg_catalog.array_agg(pg_catalog.row_to_json(ri)))
FROM (
  SELECT
    (SELECT rolname FROM pg_authid WHERE oid = usesysid) AS usename,
    application_name,
    client_addr,
    w.state,
    sync_state,
    sync_priority
  FROM pg_catalog.pg_stat_get_wal_senders() w, pg_catalog.pg_stat_get_activity(pid)
) as ri;

This is regarding Patroni--I haven't yet dug into that source to see how long that timeout is. PG 13.3, monitoring did
notshow heavy load nor unusual lock activity around when this happened.