I’m having this problem on all my sites (each site uses a different theme) that are using the lastest installation of WP. Each site is on it’s own server and each has its own database. I have tried deleting the default theme but came up with my site disappearing altogether when it reverted back to the default theme, even though it wasn’t there. It also got rid of the theme I was using. Ended having to reinstall the theme. I will try the suggestion with the plugin and will post my findings here.