Control Panel Session 60 second Timeout
I've had issues before where I was getting logged out and could not fathom why: it turned out (after weeks) that when I was using Inspector Tools' Responsive Design mode, Chrome sends different UA strings... which by default causes Craft to log the user out.

It's a long shot; but see if you're only experiencing the issue when you've got your inspector open and in mobile device simulation / responsive design modes.

The fix for me was to add the following to config/general.php

'requireMatchingUserAgentForSession' =&gt; false, // stop Craft logging you out of the CMS while using Chrome's "Device Mode" view for responsive development