Whoever it is, it's not us... as @pitaj suggests it could be bots issuing HEAD requests to determine site availability before crawling? Who knows... I am looking at some of them coming in our logging system now, but they have no user agent either, so 🤷
In my topic.tpl I made some changes using @first to separate first post in topic from others. It worked, but there is now next problem. When i create a new post it doesn't show it instantly, I have to refresh page to see that post.