Permit access based on Client IP "again"

What's happening is that the "drop" command in your iRule will get executed for all requests. I suspect that you may be used to 4.x iRules, where the "pool" command would stop execution of the iRule; in 9.x, processing will continue.

The following iRule should do what you want:

when CLIENT_ACCEPTED {
  if { [IP::addr [IP::client_addr] equals 10.10.10.10] } {
    pool pool-my-pool
  } else {
    drop
  }
}