Redirect loop served from cache
X-Drupal-Route-Normalizer: 1


That's either the redirect module or the corresponding core patch, I guess the first.

There have been a bunch of bugs in the past about this but it should work now if you update to the latest version.

This for example someteimes happened with different url query parameters, or a trailing ?, e.g. "some/url?", redirect.module redirected that to /some/url but the page cache in Drupal core actually cached it for a normalized URL without ?, so it cached a redirect to /some/url as /some/url, and then you have your redirect loop.

If you can still reproduce with the latest redirect version, then open a bug report. Also make sure that you are not using a Drupal 7-style configuration for nginx (that e.g. adds a ?q=path qery parameter)