Sticky Sessions / Tomcat Session Persistence (Blue/Green)

Help!
1

Hi,
I am trying to setup a Blue/Green zero downtime architecture.
I am using HAProxy and 2 Tomcats and a separate Redis server for a central storage of the session
(I introduced Redis to test, I was using initially just Tomcat to storage and replicate the sessions and I was getting the same behavior described below anyway).

This is my HAProxy config:

global
    ssl-default-bind-options ssl-min-ver TLSv1.2
    maxconn     20000
    log         127.0.0.1 local0
    user        haproxy
    chroot      /usr/share/haproxy
    pidfile     /run/haproxy.pid
    daemon
    # turn on stats unix socket
    stats socket /var/lib/haproxy/stats level admin

frontend stats
    bind *:80
    mode http
    stats enable
    stats uri /stats
    stats refresh 10s
    stats admin if TRUE

frontend  main
    bind :443 ssl crt /etc/ssl/certs/tomcat/cert.pem

    maxconn     8000
    timeout     client  30s

default_backend             app

backend app
    mode        http
    cookie      JSESSIONID prefix nocache
    option      httpchk
    option      redispatch
    option      http-keep-alive
    timeout     connect 1s
    timeout     server  30s
    balance     roundrobin
    server app1 172.31.1.41:443 cookie app1 check ssl verify none
    server app2 172.31.1.42:443 cookie app2 check ssl verify none

What I would like is this:
1.- User initiates Connection to app1 backend
2.- I disable app1 or app1 server goes down
3.- User gets moved to app2 without loosing his session
4 .- I enable or bring up app1 server
5.- User gets moved to app1 server without loosing his session (I dont mind disabling/stoping app2 temporarly to force the migration if neccesary)

What is happening currently:
1.- User initiates Connection to app1 backend
2.- I disable app1 or app1 server goes down
3.- User gets moved to app2 without loosing his session
4 .- I enable or bring up app1 server
5.- User is brought back to login screen

Just for additional info on my current setup
I am not using AJP (mod_jk workers configuration) for the tomcats because I want to avoid using AJP if possible.

At this point I am a bit lost on what is causing this and how to troubleshoot, if there is anyone that can give any advice or have any ideas they will be greatly appreciated and more than welcome.

Thanks for reading.