Case: a suspected 'shadowban' was a 19% seasonal reach dip

Case: a suspected 'shadowban' was a 19% seasonal reach dip
A lifestyle account (88k) reported a sudden reach crash. 90-day audit, n=120 posts.
— 'Crash' period median reach: 9,600 (10.9%)
— Prior 90 days: 11,850 (13.5%)
— Year-prior same weeks: also -17% — a recurring August trough
— Hashtag-search visibility: intact across all test tags
No penalty existed; it was a calendar effect mistaken for suppression.
So what: before debugging a 'shadowban,' compare to the same window last year — most crashes are seasonality plus regression to the mean. (n=120 posts, 90-day audit)