Hello,
Thank you very much for choosing our theme and for contacting us.
Please check and follow this manual: https://xtemos.com/docs-topic/update-the-theme/
if the problem remains, insert the site admin access into the Private content below the message area. We will take a closer look at the case.
Please, confirm the permission for plugin deactivation, and switching to the parent theme. As soon as we complete the testing we will enable all back, however, the site would be without plugins for 15-20 min. You would better make the full backup of your site.
Best Regards