Upgrading Drupal

I haven't worked with drupal for about 4 years now so I need some help. Was contacted by old workplace with the request to help with upgrade.

Hello all,

One of our Drupal 7 website has been hacked after critical vulnerabilities :

   https://www.drupal.org/sa-core-2018-003
   https://www.drupal.org/sa-core-2018-004

I disconnected the server and I am currently reinstalling the website is reinstalled on a freshly installed server.

My questions are :

Taxonomy search failed and had to restore 8.5.2

I have to upgrade a site from  from Drupal 8.3.7 to Drupal 8.5.3 but I am getting following drush error when I clear cache. Any  help?

Error: 

 [error]  Drush command terminated abnormally due to an unrecoverable error.
Error: Class 'Drupal\Core\Session\AccountInterface' not found in /var/www/html/web/core/includes/bootstrap.inc, line 83
 

Current Version:

Drupal: 8.3.7 to 8.5.3

Drush version : 9.2.3

Composer version:

Composer version 1.6.5 

Thank you

Rao

After updating to version 7.59 the option to respond the comments has disappeared. How can I do?

i have made custom theme and i use like

{{ content.field_contact_details }} 

to display content field, but after update form 8.4.5 to 8.5.3 all field content in theme not work and disappeared from site.