Data loss is happened while migrating the database from mysql5.7.42 to mariadb10.3.39

Hello Team,

We are planned to upgrade the OS from ubuntu 18.04 to ubuntu 20.04. In the same server we have the mysql-5.7.42 DB(Dedicated). As part of ubuntu upgrade we planned to migrate the database also from mysql to mariaDB(Because of some application dependencies). So , after the upgrade we have installed the mariadb and tried to restore the backup . Restoration is completed successfully. But we found there are some data loss happened during the restoration(Based on the row count)

*mysql> select sum(table_rows) from information_schema.tables where table_schema = 'bugzillaapp_DB' ;

+-----------------+

| sum(table_rows) |

+-----------------+

|         3399283 |

+-----------------+

1 row in set (1.43 sec)

*MariaDB [(none)]> select sum(table_rows) from information_schema.tables where table_schema='bugzillaapp_DB';

+-----------------+

| sum(table_rows) |

+-----------------+

|         2705944 |

+-----------------+

1 row in set (0.003 sec) 

Kindly help me on this, this is a very critical one because ubuntu18.04 is going to stop their support by 31May.