Monitor two pool maintenance page iRule using XFF not working...

before working on this, it's very similar to your other one and I was curious if this is on the same virtual? If so, is the other logic in this rule as well or a different rule? 

I am not sure if the new site is formatting your iRule incorrectly or what but, it does not appear that the iRule will function as you want in the state I see it right now.

There are several things wrong with the logic so I am re-posting it here with clearing formatting and commented with the logic as it is:

when HTTP_REQUEST {
    set CHECK_IP [lindex [lsearch -all -inline -not -exact [split [HTTP::header values X-Forwarded-For] "\{\} ,"] {}] 0] 
    # Check if userds are NOT in internal user DG
    if { !([class match -- $CHECK_IP eq DG-INTERNAL-USERS-XFF]) } {
        # Check if uri is in allowed list
        if { [class match -- [HTTP::uri] eq DG-ALLOWED-URI-LIST] } {
            #blocks external users (i.e. IPs  Not in Interal Users DG)
            reject
            log local0. "Client IP Discard: \ [HTTP::host][HTTP::uri]->[IP::client_addr]" 
        }
        # Check if External Pool has zero active members
        if { [active_members EXTERNAL-POOL] < 1 } {
            #IF so, check if they are "external" users (i.e. NOt in Internal users DG 
            if { !([class match -- $CHECK_IP eq DG-INTERNAL-USERS-XFF]) } {
                #redirect external users to maintenance-page
                HTTP::redirect "http://maintenance-page.com/external" 
                # returns form proccessing this event ####  No other code in this iRuel will run!!!!!!!
                return
                ######  Rest of this logic will never be processed!!!!   ####################
                
                # Check if internal Pool is down
                if { [active_members INTERNAL-POOL] < 1 } {
                    # Check if IP IS in the Internal Uers group  
                    if { ([class match -- $CHECK_IP eq DG-INTERNAL-USERS-XFF]) } {
                        #  redirect internal users to the maiantinace page if the internal pool is down
                        HTTP::redirect "http://maintenance-page.com/internal"
                        # returns form proccessing this event ####  No other code in this iRuel will run!!!!!!!  But we would never get this far anyway.
                        return
                        ######  Rest of this logic will never be processed!!!!   ####################
                        
                        # Send traffic to external pool
                        pool EXTERNAL-POOL
                    # IF you are NOT in Internal Users DG
                    } else {
                        # Send to Internal Pool
                        pool INTERNAL-POOL
                        log local0. "the X-Forwarded-For header value is $CHECK_IP"
                    }
                }
            }
        }
    }
}

It is diffiucult to tell from the current logic exactly what you were trying to accomplish But this is my best guess at what it SHOULD look like:

when HTTP_REQUEST {
    set CHECK_IP [lindex [lsearch -all -inline -not -exact [split [HTTP::header values X-Forwarded-For] "\{\} ,"] {}] 0] 
    # Block external IPs form getting to ALLOWED-URI-LiST
    if { !([class match -- $CHECK_IP eq DG-INTERNAL-USERS-XFF]) } {
        if { [class match -- [HTTP::uri] eq DG-ALLOWED-URI-LIST] } {
            reject
            log local0. "Client IP Discard: \ [HTTP::host][HTTP::uri]->[IP::client_addr]" 
        }
    }
    # If External Pool is down, redirect enternal users, and send internal users to Internal Pool
    if { [active_members EXTERNAL-POOL] < 1 } {
        if { !([class match -- $CHECK_IP eq DG-INTERNAL-USERS-XFF]) } {
            HTTP::redirect "http://maintenance-page.com/external" 
            return
        } else {
            pool INTERNAL-POOL
            log local0. "the X-Forwarded-For header value is $CHECK_IP"
        }
    }
    # Check if Internal Pool is down, redirect External users to maintiencace page, and allow everyone else to External Pool
    if { [active_members INTERNAL-POOL] < 1 } {
        if { (![class match -- $CHECK_IP eq DG-INTERNAL-USERS-XFF]) } {
            HTTP::redirect "http://maintenance-page.com/internal"
            return
        } else {
            pool EXTERNAL-POOL
            log local0. "the X-Forwarded-For header value is $CHECK_IP"
        }
    }
}