The proftpd has been fixed as you suggest but the upgrade could went on further until this error showed up.
ERROR while trying to (to insert upgrade info into history table), the query was: INSERT INTO upgrade_history (upgrade_date, version_info, os, update_ticket, mu) VALUES (now(),
'18.0.21', 'CentOS 6.9', '', '0')
Check the error reason (see log file: /var/log/plesk/install/plesk_18.0.21_installation.log), fix and try again
***** problem report *****
ERROR while trying to (to insert upgrade info into history table), the query was: INSERT INTO upgrade_history (upgrade_date, version_info, os, update_ticket, mu) VALUES (now(),
'18.0.21', 'CentOS 6.9', '', '0')
[2019-11-19 23:13:53.805] ERR [panel] DB query failed: SQLSTATE[42S02]: Base table or view not found: 1146 Table 'psa.PanelNotificationTemplateSettings' doesn't exist, query was: DESCRIBE `PanelNotificationTemplateSettings`:
0: /usr/local/psa/admin/plib/Db/Adapter/Pdo/Mysql.php:60
Db_Adapter_Pdo_Mysql->query(string 'DESCRIBE `PanelNotificationTemplateSettings`')
1: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Adapter/Pdo/Mysql.php:171
Zend_Db_Adapter_Pdo_Mysql->describeTable(string 'PanelNotificationTemplateSettings', NULL null)
2: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Abstract.php:836
Zend_Db_Table_Abstract->_setupMetadata()
3: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Abstract.php:875
Zend_Db_Table_Abstract->_setupPrimaryKey()
4: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Abstract.php:983
Zend_Db_Table_Abstract->info()
5: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Select.php:100
Zend_Db_Table_Select->setTable(object of type Plesk\Db\Table\Broker\PanelNotificationTemplateSettings)
6: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Select.php:78
Zend_Db_Table_Select->__construct(object of type Plesk\Db\Table\Broker\PanelNotificationTemplateSettings)
7: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Abstract.php:1019
Zend_Db_Table_Abstract->select()
8: /usr/local/psa/admin/plib/vendor/plesk/zf1/library/Zend/Db/Table/Abstract.php:1376
Zend_Db_Table_Abstract->fetchAll(string '`code` = 'panelUpdateError'', NULL null, NULL null)
9: /usr/local/psa/admin/plib/Db/Table/Abstract.php:144
Db_Table_Abstract->findByField(string 'code', string 'panelUpdateError')
10: /usr/local/psa/admin/plib/Db/Table/Abstract.php:156
Db_Table_Abstract->findOneByField(string 'code', string 'panelUpdateError')
11: /usr/local/psa/admin/plib/Db/Table/Broker/PanelNotificationTemplateSettings.php:13
Plesk\Db\Table\Broker\PanelNotificationTemplateSettings->findOneByCode(string 'panelUpdateError')
12: /usr/local/psa/admin/plib/PanelNotification/Settings/PleskTemplateSettingsRepository.php:26
Plesk\PanelNotification\Settings\PleskTemplateSettingsRepository->getSettings(string 'panelUpdateError')
13: /usr/local/psa/admin/plib/PanelNotification/Settings/TemplateSettingsRepository.php:33
Plesk\PanelNotification\Settings\TemplateSettingsRepository->getSettings(string 'panelUpdateError')
14: /usr/local/psa/admin/plib/PanelNotification/Filters/FiltersChecker.php:24
Plesk\PanelNotification\Filters\FiltersChecker->check(string 'panelUpdateError', object of type Plesk\PanelNotification\Templates\Template, object of type Client)
15: /usr/local/psa/admin/plib/PanelNotification/Manager.php:73
Plesk\PanelNotification\Manager->send(string 'panelUpdateError', object of type Client, array)
16: /usr/local/psa/admin/plib/CommonPanel/Update/Notifier.php:152
Plesk\CommonPanel\Update\Notifier->sendError()
17: /usr/local/psa/admin/plib/CommonPanel/Update/Notifier.php:81
Plesk\CommonPanel\Update\Notifier->notifyAboutUpdate(boolean false)
18: /usr/local/psa/admin/plib/scripts/update-failure-notification.php:7
ERROR: Plesk\Exception\Database: DB query failed: SQLSTATE[42S02]: Base table or view not found: 1146 Table 'psa.PanelNotificationTemplateSettings' doesn't exist, query was: DESCRIBE `PanelNotificationTemplateSettings` (Mysql.php:60)
Error: An error occurred during performing of installation POST actions (see log for details).
Warning! Not all packages were installed.
Please check if your system services are operable.
Please resolve this issue and try to install the packages again.
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