When trying to browse through the Web Gateway, you see a Read Timeout error for some websites.
The most likely cause is that the web server hosting the website will not respond to HTTP 1.0 requests. You can verify this with Internet Explorer's Advanced settings which allows you to disable HTTP 1.1 as shown here:
Once you uncheck the box and bypass the SWG proxy, try accessing the website again. If you still receive a timeout error, the website's server is rejecting HTTP 1.0 requests.
The Web Gateway proxy only sends HTTP 1.0 requests. The only options in this case are for the web server's administrator to disable the setting blocking HTTP 1.0 or to bypass the Web Gateway when browsing to that website.