CLIENT_CONNECTED still supported in 11.5.3

As @Odaah suggests, there is no CLIENT_CONNECTED event. The CLIENT_ACCEPTED event fires when the client traffic is accepted for processing (for TCP, on completion of a successful three-way handshake with the client; for UDP, on receipt of a segment; and so forth). The SERVER_CONNECTED event fires when the layer4 session setup completes toward the destination (for LTM, that's usually a pool member). In other words, for TCP, it's when the server-side three-way handshake successfully completes; for UDP, it's when the first segment in the flow has been transmitted; and so forth.