You may need to reload your messages page after going to it for the new message(s) to appear instead of it showing you your old, read messages. If I have old messages that have been marked as read but that I haven't yet deleted and I then get a new message, clicking my 'messages' button in the top right to go to my messages page will only result in those old, read messages displaying for me. I must then refresh the page while viewing these old messages for the actual new message(s) to then be shown instead of the old, read messages. I'm not sure what is the source of the issue (the site, my browser, a setting, etc.), but it has been like that for me since I joined so I'm used to just having to go to messages and then reload that messages page to get the new message(s) to appear.