Failed to upgrade from 10.3.9 to 10.4.7

Failed to upgrade from 10.3.9 to 10.4.7

Scenario 1:
Follow normal procedures:
1. install 10.4.7.
2. Start MariaDB on the 10.3.9.
3. Run mysql_upgrade and everything is OK.
4. Restart MariaDB but it hangs. No socket file is generated. "mysqld.err.upgrade" is attached for reference.

Scenario 2:
Use export/import method:
1. install 10.4.7.
2. Start MariaDB on the 10.3.9.
3. Run mysql_upgrade and everything is OK.
4. Run mysqldump to export user database and 'mysql' database data.
5. Run mysql_install_db to create a new a new 'empty' MariaDB server.
6. Import the user database data into the new MariaDB server and restart it sucessfully.
7. import the 'mysql' database data into the new MariaDB server. "mysql_data.sql" is attached for reference.
8. Restart the new server but it hangs. same symptom as scenario 1, no socket file is generated. "mysqld.err.dump" is attached for reference.
9 It can restart MariaDB successfully with --skip-grant-tables option.

It seems that mysql_upgrade cannot ensures that the system tables in the mysql database are fully compatible with the new version. "my.cnf" is attached for reference.

Please advise how to solve the upgrade problem.