Yes, seems it can’t connect to db so remove it manually and reinstall roundcube using these commands:
mysql -uroot -e 'DROP DATABASE IF EXISTS roundcube'
mysql -uroot -e 'DROP USER 'roundcube'@'localhost''
rm /var/lib/roundcube/index.php
Now install roundcube again:
v-add-sys-roundcube
Change perms:
chown -R hestiamail:www-data /etc/roundcube/
find /etc/roundcube/ -type f -iname "*php" -exec chmod 640 {} \;
chown -R hestiamail:www-data /var/lib/roundcube/
chown -R hestiamail:www-data /var/log/roundcube/