If the editor does not load when you open up a project please go through the following list for possible solutions;
Try emptying cookies and cache
Remove all cookies and cache from previous editors/preview windows. This is done by opening the browser's developer tools (Option + ⌘ + I on Mac, or F12 on PC, or just right-click anywhere in the browser and choose Inspect) and then click Application (or Storage or similar) and open up Cookies/Local storage/Session storage and choose your website and then find and delete the following keys;
Example of Cookies/Local storage/Session storage
Load the editor with a different starting parameter
Some websites do not allow parameters starting with a specific character (?, #). If you can't see any editor parameters in the URL try to change the starting character and see if it works better after that. You do this by clicking My websites -> click the website that your project is set up for -> click Edit website -> change parameter character and hit Save. Now try to open the project again.
Activate the editor manually
If you remove all (if any) parameters from the URL and then add ?sg-edit or #sg-edit last in the URL and then hit Enter the website will reload and try to load the Editor. If this works you will get a list of your projects for this website and you can then choose the project you want (see image).
Can you open up a preview for your project?
If you can't even open up a preview window for your project you should check if the script is implemented correctly.
Do you get any errors in the console in your browser's dev tools?
If none of the above solutions work you can open up the browser's dev tools and check the console for error messages. You do this by right-clicking in the browser window and then clicking on Inspect. This will bring up the browser's dev tools. You then need to click on the Console tab and check if there are any error messages that can explain why the editor does not appear.