A number of websites with log-ins set a timer for how long the site will stay up without user site interaction, presumably to keep server lines from getting clogged with logged-in users not really interacting with the site. For some sites, cookies are used to set a life-span for the session, and as long as the user interacts with the site, the site code/script causes the cookie to keep being updated and extending the life-span; at some point, if no more interactions occur, the expiring cookie triggers a timeout of the site. But also, if something blocks any of the cookie updating process, the timer can also run down, even if the user is still using the site. Because this is happening for all your browsers, something ahead of or affecting all the browsers may be interfering with the cookie updating (such as anti-malware, aggressive adblockers, etc).