Search.json has a key 'next' for the next page. Part of the url is missing:
https://packages.drupal.org/8/search.json?s=
"next": "https://packages.drupal.org//search.json?s=&page=2"
Should be
"next": "https://packages.drupal.org/8/search.json?s=&page=2"
Goto search url and look at bottom of document.
Fixed
1.0
Code