In this settings, you must enable READER https://www.screencast.com/t/wDliAJeBLyL
In this case, your inner posts will have amp version when you add /amp to end of url. And it's worked on your site until you disabled this option
Using Transitional - doesn't have a sense, because this mode is working ONLY if your site doesn't have any dynamic content: no price comparison, no carousels, sliders, filters, absolutely nothing except text content and simple galleries. If you want to see how this mode looks like, enable one of default wordpress themes and check your site in this mode on amp.