OperationalError pymysql.connections in _read_bytes error(2013, 'Lost connection to MySQL server during query')

Now I'm in big hard trouble because of mysql connection loss. sometimes server starts to make some mysql related errors. Develope envrioments are as following.

AWS EC2, AWS DB t2.small, MySQL(CONN MAX AGE 60sec, WAIT_TIMEOUT 300sec) Ubuntu 18, Django 1.11, Python3.6

While apscheduler threads are running, it abruptly happens while writing data on AWS mysql DB.

Thank you so much in advance!

1. pymysql/connections.py in _read_bytes at line 707

                self._force_close()
                raise
        if len(data) < num_bytes:
            self._force_close()
            raise err.OperationalError(
                CR.CR_SERVER_LOST, "Lost connection to MySQL server during query")
        return data
    def _write_bytes(self, data):
        self._sock.settimeout(self._write_timeout)
        try:

2. Django SQL query is as following:

SELECT `django_apscheduler_djangojob`.`id`, `django_apscheduler_djangojob`.`job_state` FROM `django_apscheduler_djangojob` WHERE `django_apscheduler_djangojob`.`next_run_time` <= %s ORDER BY `django_apscheduler_djangojob`.`next_run_time` ASC


OperationalError: (2013, 'Lost connection to MySQL server during query')