If you've changed a project's website and then get an alert that says "This project does not belong to this website" when you try to edit that project, you can try clearing local storage for that website to get this working.
To do this open up a preview of the project from the dashboard. Then click anywhere on the page and choose inspect (or hit F12 on a PC) to bring up the browsers development tools. Then click on the Application tab and fold out the Local storage tree and click your website. Now the key value pairs should be visible on the right.
Now locate the ones called sg_object and sg_ls_object and delete these by clicking them and then hit delete (or right click and choose remove on both of them). Now close the preview page and go back to the Dashboard and reload it. Now try Edit the project again and see if you still get the alert.
If you still get the alert please check your implementation.