The usual suspects.
When a real drop happens, it's almost always one of these four.
A Google algorithm update
Google rolls out broad core updates several times a year that reshuffle rankings. If lots of your keywords dropped at once around a known update date, this is likely it — the fix is improving quality, not chasing tricks.
A technical problem
A site that went down, got slow, accidentally added a “noindex” tag, or broke during a redesign can tank rankings fast. These are often the quickest to fix once you spot them.
Content changed or disappeared
A page that got edited, removed, or redesigned into thinner content loses the rankings it earned. Redesigns are a common silent culprit — the new site looks great and quietly dropped half the words Google was ranking.
A profile or review dip
For local rankings, a Google Business Profile that got suspended, edited, or reverted — or a slowdown in fresh reviews — can drop you out of the map pack even when your website is fine.