Comments - error : (408595) Lost connection to the master server

The idle value for all of those was around 300 seconds, what is the wait_timeout value configured on the backend servers? That error is likely caused by the server closing idle connections and the master connection was not used in the last 300 seconds.

You can set the value of connection_keepalive for the readwritesplit service to 60 seconds to keep the connection alive:

connection_keepalive=60

it's not work

+-----------------------------+----------+
| Variable_name               | Value    |
+-----------------------------+----------+
| connect_timeout             | 30       |
| deadlock_timeout_long       | 50000000 |
| deadlock_timeout_short      | 10000    |
| delayed_insert_timeout      | 300      |
| innodb_flush_log_at_timeout | 1        |
| innodb_lock_wait_timeout    | 120      |
| innodb_rollback_on_timeout  | OFF      |
| interactive_timeout         | 300      |
| lock_wait_timeout           | 86400    |
| net_read_timeout            | 30       |
| net_write_timeout           | 60       |
| slave_net_timeout           | 60       |
| thread_pool_idle_timeout    | 60       |
| wait_timeout                | 300      |
+-----------------------------+----------+
14 rows in set (0.00 sec)