The problem is not reproducing so easily, but my scenario looks like following:
- Start Windows VM
- Start IE browser
- Login as Admin
- Do not logout or close the browser
- Turn off VM with saving the state
- Start VM again
Result: VM started with browser already opened, but Admin is not logged in to Zabbix frontend and Dashboard shows widgets with "Session terminated" error. Page refresh is not helping. To log in again user needs to clear cookies.