My iRule stopped working?!

Logging will help you see what's going on.

(You shouldn't need to invert your first condition in the else clause -- it's implied when it failed the "if" part.)

I'd test with a simpler rule that includes logging at every decision point, then add conditions as necessary, again logging in each until you have it working the way you want. Start here:

when HTTP_REQUEST {
  if {[matchclass [IP::remote_addr] == $::private_net]}{
    log local0. "Matched on client IP [IP::remote_addr]"
    pool my_pool
  } else {
    log local0. "No match on client IP [IP::remote_addr]"
    pool myother_pool
  }
}

HTH

/deb