We’re experiencing a weird problem which neither our specialized hosting provider WPEngine nor several WP experts could solve so far:

Thousands of unwanted URLs/pages are created based on existing category archives that each show the complete (paginated) archive of our WP installation. All of them have a "0" in the slug, some of them in two places. Here’re two examples:

ourwebsite/category/environment/0/page/2670/

ourwebsite/category/environment/0/page/2648/0/page/2601/.

The last number is the page/pagination number. These URLs are neither created by a theme or plugin (tested with WP standard theme and no plugins installed) nor by our hosting environment (says WP Engine).

We’re only aware of these URLs because Google Search Console informed us about incorrect structured data on these pages. By now over 2500 issues are reported.

So the big question is what creates these URLs/"pages". Normally, they should result in a 404 page.

Any ideas?