Register form not responsive
I am very happy how the Flatter theme is looking on my Iphone, but I found that when you click "Register" The form did not conform to the responsive layout and was continuing off the template.
Registering people is probably the most important part of the page. If I saw that when visiting a site I would think it was broken and leave. This is a big problem because the theme would be worthless if it did not collect new subscribers.