Multiple canonicals
WarningMedium priority
Pages declaring more than one canonical.
Why it matters
Search engines may ignore all of them, leaving the page to be chosen for by something else entirely.
How to fix it
Keep one. Several usually means a template and a plugin are both adding one, so look for the second source.
Skitter runs this check on every crawl, and lists each page it finds with the evidence: the header, the tag or the link that gave it away.