I played through Tower of Riddles on my phone (Samsung Galaxy s4, chrome browser.) After the end I clicked write a comment and typed one out. Unfortunately, there was no way to submit it. There was no place to click on the screen other than the text box.
I finally gave up trying to salvage my comment and went back to see if the bug was replicable or not. I clicked on rate/comment again and that time the submit buttons did show up under the comment box. I had to rewrite a comment, but I was able to submit that time. I am not sure what happened or why the submit button didn't show up the first time around.