Rocketchat in Univention Corporate Server behind Nginx Proxy


i use Univention Corporate Server for my Webapps. Rocketchat is one App in my Case.
Univention uses Proxypass.

<IfModule mod_ssl.c>

<VirtualHost *:443>
        IncludeOptional /etc/apache2/ucs-sites.conf.d/*.conf
        SSLEngine on
        SSLProxyEngine on
        SSLProxyCheckPeerCN off
        SSLProxyCheckPeerName off
        SSLProxyCheckPeerExpire off
        SSLCertificateFile /etc/letsencrypt/live/server.domain.tld/fullchain.pem
        SSLCertificateKeyFile /etc/letsencrypt/live/server.domain.tld/privkey.pem
        SSLCACertificateFile /etc/univention/ssl/ucsCA/CAcert.pem

        #SetEnvIf User-Agent ".*MSIE.*" nokeepalive ssl-unclean-shutdown

        ### To enable special log format for HTTPS-access
        # LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\" %p" combinedssl
        # CustomLog /var/log/apache2/access.log combinedssl     ## with port number

        ProxyPass /rocketchat/ retry=0
        ProxyPassReverse /rocketchat/

Infront of my Server i use a Nginx Reverse Proxy

upstream rocketchat {

server {
    listen 443 ssl;
listen   [::]:443;
    ssl_certificate           /etc/letsencrypt/live/; 
    ssl_certificate_key       /etc/letsencrypt/live/;

    ssl on;
	ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
	client_max_body_size 20000m;

   	access_log            /var/log/nginx/chat-access.log adv;
	error_log            /var/log/nginx/chat-error.log notice;

location ^~ /.well-known { root /var/www/letsencrypt; }
    location ~ / {
        proxy_pass https://rocketchat;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
	proxy_set_header Host $server_name;

        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forward-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forward-Proto http;
        proxy_set_header X-Nginx-Proxy true;
        proxy_redirect off;

My Problem:
I can login with Webbrowser and Rocketchat Computer App. I cant login with mobile App android 4.0.2.

Any idea, how i can solve it? is something wrong?
If you need any information, please tell me