Hello
Can you please confirm to me if the issue happens if you have ONLY the Thrive Leads plugin active beside the kleo theme(if you have child theme deactivate it by activating the parent) ?
Yes.
Try to delete the theme and to re-download again and to install it again.
We can´t do it because we will lose the theme settings. It´s the last version of Kleo. This error is happening in other site with the same plugin and the same version of Kleo.
Thank you so much.