Azure SDK python client to Azure iothub over HAproxy (SSL handshake failure)

I am trying to fix an IP address for Azure Iothub via Load Balencer and HAproxy as suggested in this solution: Connection architecture I have configured the HAproxy as suggested to pass the SSL handshake to the server:

global
        log /dev/log    local0
        log /dev/log    local1 notice
        chroot /var/lib/haproxy
        stats socket /run/haproxy/admin.sock mode 660 level admin expose-fd listeners
        stats timeout 30s
        user haproxy
        group haproxy
        daemon

        # Default SSL material locations
        ca-base /etc/ssl/certs
        crt-base /etc/ssl/private

        # Default ciphers to use on SSL-enabled listening sockets.
        # For more information, see ciphers(1SSL). This list is from:
        #  https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
        # An alternative list with additional directives can be obtained from
        #  https://mozilla.github.io/server-side-tls/ssl-config-generator/?server=haproxy
        ssl-default-bind-ciphers ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:RSA+AESGCM:RSA+AES:!aNULL:!MD5:!DSS
        ssl-default-bind-options no-sslv3
defaults
        log     global
        mode    http
        option  httplog
        option  dontlognull
        timeout connect 5000
        timeout client  50000
        timeout server  50000
        errorfile 400 /etc/haproxy/errors/400.http
        errorfile 403 /etc/haproxy/errors/403.http
        errorfile 408 /etc/haproxy/errors/408.http
        errorfile 500 /etc/haproxy/errors/500.http
        errorfile 502 /etc/haproxy/errors/502.http
        errorfile 503 /etc/haproxy/errors/503.http
        errorfile 504 /etc/haproxy/errors/504.http frontend haproxy_iothub
        bind *:8883
        bind *:443
        bind *:5671
        mode tcp
        default_backend iothub
backend iothub
        mode tcp
        server iothub [Server URL]:8883 check
        server iothub [Server URL]:443 check
        server iothub [Server URL]:5671 check

To simulate the device, I used Azure V2 SDK (azure-iot-device) and defined a proxy option and created a client from a connection string.

proxy_opts = ProxyOptions(proxy_type=socks.HTTP, proxy_addr="Proxy_ IP", proxy_port=8883)
device_client = IoTHubDeviceClient.create_from_connection_string("IOTHUB_DEVICE_CONNECTION_STRING", websockets=True, proxy_options=proxy_opts )

I was not able to reach the iothub, I tried debugging the library to get more information and it turned out that the blocking occurs due to a general proxy error ("connection closed unexpectedly") in _negotiate_HTTP. socks.HTTPError :504 : Gateway Time-out (in socks.py)

HAproxy logging showes :

Oct 18 08:48:37 vmss2xigg000000 haproxy[27470]: *..:59000 [18/Oct/2021:08:48:37.451] haproxy_iothub iothub/iothub1 1/1/38 0 -- 1/1/0/0/0 0/0

Any help much appreciated

HA-Proxy version 1.8.8-1ubuntu0.11

Azure-iot-device Version 2.8.0