I have a live D8 pantheon site and keep randomly getting `index.php` in the menu link urls. It's now happened  four or five times. We've set a base url for the sitemap, so it has prevented the sitemap from including `index.php` (which it did the first time). And we've also redirected from `/index.php` to `/` in settings.php, which works fine.

But still, today, on the live site, we found that a bunch of menu links randomly had /index.php/ in the paths (it was all the links referencing a node). And if we clear the cache or just wait 20 minutes, it magically fixes itself. 

I haven't had enough time with the problem persisting to successfully debug it. This is similar to the following link, but the solution here is for apache, whereas pantheon uses nginx. https://www.drupal.org/forum/support/post-installation/2016-09-19/how-to-remove-indexphp-from-urls

Anyone ever run into this or have an idea where to start prodding next? Any help or debugging suggestions are greatly appreciated! Thanks.