[Solved] lib/pkp/lib/vendor/autoload.php missing when upgrading from 2.4.8.2 to 3.1

An update:

I tried installing OJS 3.1 from a tarball, but now I’m getting different errors when running upgrade.php:

PHP Notice: unserialize(): Error at offset 651 of 1506 bytes in /var/www/html/ojs/lib/pkp/classes/db/DAO.inc.php on line 352
PHP Stack trace:
PHP 1. {main}() /var/www/html/ojs/tools/upgrade.php:0
PHP 2. UpgradeTool->execute() /var/www/html/ojs/tools/upgrade.php:34
PHP 3. UpgradeTool->upgrade() /var/www/html/ojs/lib/pkp/classes/cliTool/UpgradeTool.inc.php:64
PHP 4. Installer->execute() /var/www/html/ojs/lib/pkp/classes/cliTool/UpgradeTool.inc.php:88
PHP 5. Installer->executeInstaller() /var/www/html/ojs/lib/pkp/classes/install/Installer.inc.php:186
PHP 6. Installer->executeAction() /var/www/html/ojs/lib/pkp/classes/install/Installer.inc.php:265
PHP 7. call_user_func:{/var/www/html/ojs/lib/pkp/classes/install/Installer.inc.php:415}() /var/www/html/ojs/lib/pkp/classes/install/Installer.inc.php:415
PHP 8. Upgrade->concatenateIntoMasthead() /var/www/html/ojs/lib/pkp/classes/install/Installer.inc.php:415
PHP 9. DAOResultFactory->next() /var/www/html/ojs/classes/install/Upgrade.inc.php:2201
PHP 10. JournalDAO->_fromRow() /var/www/html/ojs/lib/pkp/classes/db/DAOResultFactory.inc.php:104
PHP 11. ContextDAO->_fromRow() /var/www/html/ojs/classes/journal/JournalDAO.inc.php:40
PHP 12. DAO->getDataObjectSettings() /var/www/html/ojs/lib/pkp/classes/context/ContextDAO.inc.php:70
PHP 13. DAO->convertFromDB() /var/www/html/ojs/lib/pkp/classes/db/DAO.inc.php:590
PHP 14. unserialize() /var/www/html/ojs/lib/pkp/classes/db/DAO.inc.php:352

The upgrade script finishes with an error:

ERROR: Upgrade failed: DB: Table ‘review_assignments_tmp’ already exists

Again, there is no CSS style in the frontend, plus the additional database error:

DB Error: Unknown column ‘a.include_in_browse’ in ‘where clause’

Regards,
Ales