Many have written to tell me that they had problems leaving a comment on a post. I am not sure why but I suspect it's because you have not chosen an "identity." At the bottom of the comment sections there is a box that asks you to choose an identity for posting. I have a google account and post as 'Norbert.' There are other options if you click on the box. But you need one of these to do anything. When I go to my parents and use their computer, I often forget to check this and my comments disappear (I know, would be better were this to happen more frequently) never to be seen again. Here's a little primer on how to comment.
IMO, lots of that's valuable on this site has come from the very many useful comments readers have provided. They are often (almost always) more thoughtful than the posts that they are commenting on. So please keep them coming.