Having similar problems and still not working only in chrome. Firefox seems fine. Never had this problem prior to installing 18.1.2.
I use osticket only for internal purposes and no clients are logging in. Although I activated the OAuth2 plug in, I haven't set up the functionality for any of the emails yet (which wasn't a problem before).
Primarily, I use the agent ticket webpages. After login on firefox, I correctly go to ticket/scp/index.php and no problems.
On chrome, I get the bounce back to the login page. I added the sleep (2) code to ticket/scp/index.php but still a problem on chrome. Same sproblem with sleep(1)
Any ideas?