Leave A Comment Not Working

The leave a comment link on my testimonials page isn’t working. I’ve scanned the internet and everything says to change the permalink to something else then change it back to where you had it. When I change the permalink to plain it works but then I change it back to post name it stops working. I don’t want my pages being /?p=123 I want them to be what they are.

Any ideas what’s causing this and how to fix it?