I haven't experienced this issue exactly, but I had another technical issue during my Level 2 exam. I e-mailed Academy team and they resolved my issue immediately. I would recommend contacting firstname.lastname@example.org
Yes, I had the exact same problem, it doesn't show that it's selected when you click on it, but it is considered selected anyway when you submit the response. So just put your mouse pointer on the response you want to submit and then click on Submit and it will work. Thanks!