This error means that the connection to the database server has closed unexpectedly. HAast will immediately try to reopen the connection to recover, which is why you see data still being written to the database. However, the database operation that triggered the error has failed and it’s data will not be recorded (if it operation was trying to add data).
The root cause is that your MySQL/MariaDB server is configured to automatically close the connection after a period of inactivity, and that period is too short. To solve the problem, edit the MySQL configuration file (usually /etc/mysql/my.conf and add the following:
[mysqld]
wait_timeout = 31536000
interactive_timeout = 31536000