Redirect loop
What it means
These URLs redirect in a circle, so nothing is ever served. Browsers show an error after a few hops and search engines give up on the URL entirely.
How to fix it
Find the two or more rules that point at each other, commonly an HTTP→HTTPS rule fighting a trailing slash rule, or a CMS redirect duplicating a server one. Order your rules so each URL is rewritten at most once, and prefer one canonical form (scheme, host, trailing slash) applied in a single place.
Finding it in CrawlStat
After a crawl, open Issues and pick Redirect loop. Click Show all in Pages to filter the Pages table to the affected pages, or Export affected to hand the list to whoever owns the fix. Audit ID: redirect_loop.