Durtdawber I've created a temporary admin account at your forum, and I can see that if you navigate to the extension's settings through the search sidebar, after adding a link, it disappears as you have described.
As of right now, I unfortunately don't know what is causing this because the browser console doesn't log any visible errors (I'll have a look at this later to determine the exact cause).
However, after you reload the extension settings page (e. g.: with F5 key), you are able to add a link and hit the "Save Changes" button in order to preserve them (I've successfully created a couple test links at your forum, they're safe to remove now). I think this is just some weird behaviour with the SPA Flarum uses, but further testing is required indeed. I'll let you know if I am able to find the root cause
