You are right its ajax error. From Developers console I could confirm, there is a error saying 500 internal error resource failed to load for admin-ajax.php.
I re-installed my wordpress installation. I disabled all the plugins and also switched to my default theme – twenty sixteen. Then I’m able to see the ticket in the dropdown and also select it.
The original Theme used is Divi from Elegant themes. But there is another website of my friend which I’m only handling, there I’m using the same theme, but I’m not facing problems at all. There too I have installed OpenTickets CE and things work fine.
There seems to be something wrong with my website. ??
-Agnel