HTML / XML / JS, low-level validity (cross-cutting)HighInferred
Multiple head/body elements
What it is
Duplicate structural elements.
Why it matters
Can truncate the head, dropping directives/canonicals.
How to fix it
Ensure one head and one body.
Impact
Medium-high; silent failures. Inferred.
Evidence
Head integrity affects directive processing. Google Search Central, Robots Meta Tags Specifications; Google Search Central, Consolidate duplicate URLs (canonicalization)
Sources