session time-out

Hi Catch Themes Team, As my website http://www.dsforum.jp/2017/talien2po3ek3soiwlt545kt/, some IE (IE 11) users cannot view the page but warning "session timeout". It's very curious because other IE 11 users can view the page without problem. I suggest them to refresh browser or clean cache but the issue is still remained. I wonder whether I can add some codes to extend session time or take other ways. Could you advise me what I can do to solve this issue? I really appreciate your help. Thank you, Sumiko