Hey there,
I have noticed that in the old JIRA issue screen if I were to manually type up the wiki format for say a header as shown below it will render the Wiki format correctly.
h1. I have manually added this heading
When using the new screen if I create a comment and input the above it will not render it on the front end. When inspecting the UI element there is only a <p> tag with the text. In the old screen when inspecting the element the is a <h1> tag with content.
Regards, Phil