I suddenly just had issues logging into a Zabbix instance as the Admin user and receiving only Guest permissions.
Attempting several fixes online such as clearing cookies, browser caches and looking at the rights mysql table all failed.
In the end to fix I had to add a new user via the database.
insert into users (userid, alias, passwd, type, lang, refresh, theme) values (3,'Test',md5('zabbix'),3,'en_GB','30s','theme');
After this I could login with my newly created user, the style sheets were not loading properly though I could go to the /users.php page and work my way through making an update to my new Test user (in this case I added another group) which fixed the style sheet issue.
You can now also make any change in the user admin page to the Admin user and save it which will fix the Admin account.
