direct traffic based on information from the XML request

In your irule, I can see that all pool members are hosted on the same address... so the node status is useless... you must use a pool member status instead.

I changed the irule with right configuration.

The first event is to store the default pool name in the variable

default_pool

To use it, all of services must be in the same pool. if it is wrong, you must replace in the condition

[LB::status pool $default_pool member 172.24.248.85 8580]

pool $default_pool member 172.24.248.85  8580

when CLIENT_ACCEPTED { 
    set default_pool [LB::server pool]
}

HTTP_REQUEST {
    if { [HTTP::header Content-Type] contains "xml" } {
        HTTP::collect [HTTP::header Content-Length]
    }
}

when HTTP_REQUEST_DATA {
    set msisdn [string trim [findstr [HTTP::payload] "" 8 ""]]

    switch -glob $msisdn {
        "*0" {
            if { [LB::status pool $default_pool member 172.24.248.85 8580] eq "up" } {
                pool $default_pool member 172.24.248.85  8580
            } else {
                pool $default_pool member 172.24.248.85  8680
            }
        }
        "*1" {
            if { [LB::status pool $default_pool member 172.24.248.85 8680] eq "up" } {
                pool $default_pool member 172.24.248.85  8580
            } else {
                pool $default_pool member 172.24.248.85  8680
            }
        }
        default {
             send to a default pool or node
        }
    }  
}

Another solution is to create one pool per msisdn condition with two pool members and priority group activation.

the irule become:

HTTP_REQUEST {
    if { [HTTP::header Content-Type] contains "xml" } {
        HTTP::collect [HTTP::header Content-Length]
    }
}

when HTTP_REQUEST_DATA {
    set msisdn [string trim [findstr [HTTP::payload] "" 8 ""]]

    switch -glob $msisdn {
        "*0" {
            pool msisdn0
        }
        "*1" {
            pool msisdn1
        }
        default {
             send to a default pool or node
        }
    }  
}