How to provide the “Privacy policy link” correctly on EU COOKIE COMPLIANCE module?
Actually it's better you'd report issues like that on drupal.org and not here on Drupal Answers.

The recent EU Cookie Compliance updates happened in a rush when during the ongoing development a security hole was found. Because of that a lot of half-ready new features got released.

It happens I just released a patch which may be related to your problem, see https://www.drupal.org/project/eu_cookie_compliance/issues/2985543.

But you may not necessarily need the patch. All you need to do is to update to the latest version, then go to the module's config page and choose a method (default, opt_in etc.). Choose default to turn back to the initial method before the most recent updates added additional methods.

If that doesn't work try to follow the steps from https://www.drupal.org/project/eu_cookie_compliance/issues/2985613#comment-12685609 which was a fix for the 7.x branch but may apply for D8 as well.



Last but not least, double-check that the link you provided either goes to an existing internal route or is an external link.