Stop processing iRule by referencing a variable

Can you try this for your first rule and then add a log statement to your second iRule to see if it is successfully avoided altogether?

priority 300
when HTTP_REQUEST { 
    if { [string tolower [HTTP::path]] starts_with "/staging" } { 
        if { !([matchclass [IP::client_addr] equals IP_private_access])} { 
            log local0. "Source address [IP::client_addr] not from Private pool, session discarded" } {
            discard 
            event disable all
            return
        }
    }
}

Aaron