My proposed solution handled http to ws and https to wss correctly, whereas your template does not. Why did you change it? You should keep my solution.
Please post the manual matterhost-reverse-proxy.conf. Maybe matterhost needs some very special rules, which are not handled from either the original reverse-proxy nor my change, but this would be no argument for not adopting my change, since my proposition just solves most typical websockets proxy pass with no negative effects.
If you have to do a manual configuration for matterhost before my change, you are not doing worse with my change, because the Nethserver reverse-proxy-settings are to weak in both cases. But all the configuration for reverse-proxies were my change solves the problem do not need a manual configuration any more.
My change definitly works with webtop, because I am using it and created the change extra for webtop. If it does not work with your server, you might have run into the same bug as me. See Reverse proxy subdomain to secondary application Nethserver