There is an extra colon in the hostname when there is no port info. This is an upstream bug in the HttpFoundation Symfony component. I have filed an issue to the Symfony community to fix it.
An alternative to this is to fix it in Drupal/Core/Routing/UrlGenerator.php. Both methods should fix the error, we need to figure out which one (and pay attention to the Symfony issue resolution).
Symfony issue: https://github.com/symfony/symfony/issues/8540