This error message:
PHP Fatal error: Uncaught Error: Call to a member function getOption() on null in /var/www/ojs/cache/t_compile/480451dc2b75b35c64354d7c4cad1157538fd42d^e64e579388e5615e11e939b12134d6ae8679eba6_0.app.frontendpagesindexJournal.php:37\n
Looks the same as in this issue: Error with smarty? User Interface loaded with error message after OJS migration (3.1.1.0 -> 3.3.0.3)
Switching the theme and clearing the cache might help. It’s website appearance settings and site administration page.
This looks like a problem with data in the users table - the entries regarding a reviewer are missing. This SQL query may show if it’s true and IDs of missing users:
SELECT review_assignments.reviewer_id FROM review_assignments LEFT JOIN users ON review_assignments.reviewer_id = users.user_id WHERE users.user_id IS NULL
But, as I see from an upgrade script, this should result in a fatal error during upgrade, so not sure.