Some of the older additions that used external links are using URLs with HTTP rather than HTTPS, which seems to be causing some issues. I'm going to have to fix them one by one, which will be arduous and take some time, but it's on the To Do list! In the meantime, feel free to report any non-working links like that, and I'll get to them first. You can also copy the link, paste it in the address bar, and change http to https.