What is a canonical issue?

[Madaboutdm1719]

Canonical issue is when the server serves two or more URLs that point to the same resource without a proper <link rel='canonical'> or 301 redirect, causing the crawler to split page rank, fire duplicate‑content flags, and break cache keys.

It pollutes the request‑response cycle, forces sanity‑checks in the routing layer, and can blow up your SEO metrics.