Nothing will Update

When I add or make changes to posts or pages I update and publish them and it confirms they have been updated but then when I try to view the page the pop up comes up with the choice to ‘stay on page’ or ‘leave page’ saying content is not saved and if I leave content may be lost. If I leave the page the preview of the post is shown on the site but clicking on ‘read more’ takes me to a page that says error 404 has occured.