Local rankings blend proximity, relevance, and prominence — and drops usually trace to: a competitor got stronger (more reviews, better profile), Google re-weighted the map for that search, your profile lost signals (lapsed posts, unanswered reviews, category edits), or a suspension/edit flag you haven't noticed.
Check the boring causes first inside your GBP dashboard: pending edits, category changes, new owner-quality issues. Then compare the businesses now above you — more recent reviews and more complete profiles usually tells the story.
Recovery is unglamorous: complete every profile field, restart review velocity, answer everything, post occasionally. Local SEO is a consistency contest wearing an algorithm costume.