I am wondering you are hitting an issue we found out recently. We recently found a bug in the way the path to the static resources is calculated. Can you try to use a slash at the end of your target path?
Something like:
<Virtualhost *:80>

    ServerName streamlit.group.pt
    ServerAlias srcapp.sc.pt

	documentroot /var/www/example.com/html

	RewriteEngine On

	RewriteCond %{HTTP:Upgrade} =websocket
   	RewriteRule /test1/ ws://localhost:8501 [P]

   	RewriteCond %{HTTP:Upgrade} !=websocket
   	RewriteRule /test1/ http://localhost:8501 [P]

   	ProxyPassReverse /test1/ http://localhost:8501

</VirtualHost>

The you would have to access any app with a trailing slash: http://streamlit.group.pt/test1/ 2
Let me know if this work. Will gave you a link to this bug as soon as I file it.
Also, can you send me a snapshot of your networking tab on Chrome?
Thanks,
Matteo