Running Home-Assistant behind HAProxy and all working so far very good using the official docs one problem remained: configuration was nearly impossible using the proxied connection because the site was refreshing in regular time intervals which lead to major problems when using Node-Red or VSCode addins because a refresh without a safe before reset all the changes.
A solution was found here: https://community.home-assistant.io/t/lovelace-refreshes-refocusses-page-frequently/87446
The backend in HAProxy has to increase the timeout for tunnel connections, Home-Assistant uses WebSockets.
So using „timeout tunnel 1h“ or higher solves the problem.