In your reverse proxy settings, if you have selected the HTTP protocol,
then that means that your connections transit on port 80.
But by default the remote app client connects via port 443.
This problem can occur if you use a different port than 443 for your HTML5 connections.
Indeed, port 443 is used for connections via the Remote App web client.
You can specify a different port by editing the remoteapp2.js file with notepad,
which is located in C:\Program Files (x86)\TSplusClients\www\software :
// Remote Desktop Server
var remoteapp2_server = '';
var remoteapp2_port = '443';
Replace the value 443 by 80
// Remote Desktop Server
var remoteapp2_server = '';
var remoteapp2_port = '80';
It will be necessary to stop the web server and restart it from the home tab of the AdminTool :
and if the changes have not been taken into account on the client side,
in the web browser do a refresh with ctrl + F5 to delete the browser cache.