tmsh LTM connection table

Not at all, it's just that at any point in time there will be connections that haven't yet been load balanced. Additionally, there are other reasons such as the TCP 3 way handshake may not have completed client side, an iRule may be processing the connection (sending a redirect for instance), the response may be served from cache (so no need for a server side connection) and so on.

I'm not surprised you are seeing lots of entries like this under high load.