If Send feedback does not appear

Troubleshooting

The button is missing when Snaglist is not loaded, not started, or deactivated. Check each in turn.

Steps

Open the browser's developer console on the page and enter Snaglist. If it says it is not defined, the file did not load: check the script tag's address opens the file.
Enter Snaglist.isUserEnabled(). If it says false, the button was deactivated in this browser. Type Snaglist.setUserEnabled(true), then reload the page.
Check the Snaglist.start() call runs and has no enabled: false. With the script tag only, check it has data-github, data-email, data-endpoint or data-start.
Check the console for a Content Security Policy message. If there is one, read step 6 of Host Snaglist on your own server.
Check nothing on your page covers the corner the button sits in. To move it, set launcher: "bottom-left", or set launcher: false and open it from your own menu with Snaglist.open().