After completing the installation of your Sizefox | Connect theme app extension, a hyperlink called Manage App is displayed in the contextual menu (see image).
This is a known bug by Shopify, and by clicking on this link, you might be redirected to a nonexistent section of your admin app. Shopify and Sizefox are currently working together to fix this.
Most importantly, note that this does not prevent you from installing Sizefox | Connect properly and offer sizing recommendations to your shoppers.
