It was a weird issue. I looked a bit about it and there might be a possibility caused by installing a contrib module but in some cases it just appeared on some websites after a Drupal core update.
In any case the quick fix was either to clear caches or to go to https://yourwebsite.web.cern.ch/update.php and run the updates if any. If not just click on ok and go back to the website.
I did this on your wesbite and the links were fixed.