Post-Migration Ranking Collapse: No Diagnostic Tool Tells You What Actually Broke After a Host/Domain/Platform Switch

Summary

A business ranked top 1–3 for its state-level keywords, migrated hosting and domain from Weebly to another platform, and fell off the map entirely — no local pack presence, lost rankings, and the owner is 'at a loss,' manually poking around Google Search Console and the site backend with no idea what is wrong. This is the classic migration blind spot: an audit is run *before* the move, but nothing re-runs the full check *after* it and diffs the two states to isolate the regression (broken 301 chains, lost canonicals, dropped schema/local structured data, orphaned URLs, lost hreflang, new noindex tags, CWV regressions, NAP/GBP disconnection). Generic SEO checkers show current issues in a vacuum — they cannot say 'this specific check passed before your migration and fails now,' which is the only output that would actually fix the problem. Every week without a diagnosis is lost revenue and compounding authority loss, and non-technical site owners cannot self-diagnose it. Free and mid-tier tools have no before/after migration diffing, making this a severe, monetizable, unsolved gap in the SEO checker space.