SSH into the Synology Server.
Open the file:
/volume1/@appstore/MariaDB10/usr/local/mariadb10/etc/my.cnf
Edit the line:
[mysqld] max_allowed_packet = 1M
with the # bytes or M that you desire.
Save changes and restart the MariaDB service OR reboot the Synology:
/usr/syno/bin/synopkg restart MariaDB