irule Troubleshooting:

just for information we fixed the problem with a uri check to verify, if the client wants to load additional content for the page or if it is the first request to get the maintenance page.

if { [active_members pool_wartung] > 0 } {

                    switch -glob [string tolower [HTTP::uri]] {
                    "/directory/*"  {   
                            pool pool_wartung
                            }
                    default {

                            pool pool_wartung   
                            HTTP::uri "/wartung.html"
                        }
                    }