Only treat 406s as critical when a full browser UA or a recognized crawler UA is blocked. If the 406 is limited to bare/generic scripted UAs, that is usually expected WAF behavior and should be labeled as a monitoring nuance instead.
Wrong internal links and dead categories waste crawl flow and create weak UX/trust signals.
If 5xx endpoints start appearing in scans, they should be treated as urgent because they hurt users and crawlers fast.
Homepage, robots, sitemap files, sample products/categories, 406 counts, 404 counts, and any new 5xxs by URL + timestamp.