iRule cookie persistence and pool redirect

Hi all, base on the on below setup...

• When Pool A/NodeA1 goes down, we expect URI /beta/ requests to be sent to Pool B, as nodeA2 can't accept URI /beta/ requests.
• However, when Pool A/NodeA1 goes down, we see the LTM sending URI /beta/ requests to Pool A/nodeA2.
• F5 support said cookies have precedence over iRule and the cookie will try to honor it's persistence, hence why traffic is still being sent to Pool A / nodeA2(A1 is down at that point).

Strangely in lab I have a different behavior from the LTM.  Whether it's an new or a subsequent request, the source_addr persistence record will show the connection for 3mins(default timeout value).  During that time pressing F5 and CTRL-F5 will force the client's browser to reinitiate the communication.   When I reinitiate, despite having received a cookie, previously, for Pool A / nodeA1 -- I also get a new cookie for Pool B / node B1 and connect to node B1 successfully.  That behavior is what I'm expecting in production, but that's not the case.

Should I be adding more to the iRule, in order to maninpulate the cookies, or any suggestions of what can be at cause?

SETUP
LTM contains:
- cookie persistence with fallback source_addr
- Pool A with member nodeA1(priority 15 ) & nodeA2(priority 5); with min-active 1
- Pool B with member NodeB1 only

nodeA1 = 10.10.10.1
nodeA2 = 10.10.10.2
nodeB1 = 10.20.20.21

And an iRule that should mainly redirect like this:
if { PoolA/nodeA1 is down + URI equal "/beta/"} {
         then send it to Pool B
          }
else { send it to Pool A }

Here is the iRule:

when HTTP_REQUEST {
set sslex 0

if { ([string tolower [HTTP::uri]] starts_with "/beta/") && ([LB::status pool Alpha-Pool member 10.10.10.1 443] eq "down") } {
set sslex 1
set sni_value "betaServer.lab.com"
HTTP::header replace Host "betaServer.lab.com"
set uri [string map -nocase {"/beta /" "/"} [HTTP::uri]]
HTTP::uri $uri
pool Beta-Pool
} else {
set sslex 0
set sni_value "lab.com"
pool Alpha-Pool
} }

when SERVERSSL_CLIENTHELLO_SEND {
# SNI extension record as defined in RFC 3546/3.1
# https://support.f5.com/csp/article/K41600007
if { $sslex > 0 } {
SSL::extensions insert [binary format SSScSa* 0 [expr { [set sni_length [string length $sni_value]] + 5 }] [expr { $sni_length + 3 }] 0 $sni_length $sni_value]
}
}