iRule to direct specific IPs to specific members, not working as expected.

Agree with JPV - if you use cookie and source IP you are asking for trouble - the first request of an HTTP 'session' never has a cookie, so source IP will always be used!!

The problem is that your pool selection is being done in CLIENT_ACCEPTED, but oneconnect means that the pool is reset to the default each time HTTP_REQUEST is triggered, in addition, I think there is a slightly better way than your pool ISIS-Web_SSL member statements. I would use another pool for the webmethods traffic;

pool ISIS-Web_SSL_webmethod {
    lb method member observed
    snat disable
    monitor all https1.0
    members {
        10.10.10.108:5004 {priority 3}
        10.10.10.110:5004 {priority 1}
    }
}

and then your iRule would become;

when HTTP_REQUEST {
    if { [class match [IP::client_addr] equals "TXHUB_IP"] } {                
        persist none
        pool ISIS-Web_SSL_webmethod
    }
}