Extremely frustrating - traffic isn't processed by iRule

You are doing an event disable all in the event of redirecting due to the site being down, assuming you are using this to prevent other iRules from triggering once against that request.

This could be an issue as all future HTTP request from the same connection will not be processed by any iRules as not events will be triggered.

Configure the following LTM traffic policy and assign to the Virtual Server to ensure all events are enabled for each HTTP request hitting the Virtual Server even if from the same TCP connection:

ltm policy /Common/tcl_event_enable_all {
    requires { tcp http }
    rules {
        enable_all {
            actions {
                0 {
                    tcl
                    set-variable
                    expression "tcl:[event enable all]"
                    name eventEnableAll
                }
            }
            ordinal 1
        }
    }
    strategy /Common/first-match
}