The first diagnostic step on any Amazon Ads account review is sorting every campaign by ad spend, not by ACOS or sales. This surfaces where the budget is actually concentrating before evaluating whether that spend is converting well.
Most accounts show the bulk of spend concentrated on the top five to 10 keywords — a spend-side expression of the Keyword Concentration Principle (Top 3–5 Keywords Drive 80–90% of Sales). Auditing top-down by spend catches runaway broad/auto keywords and mis-sized campaigns before subtler issues (like Time-in-Budget Diagnostic (Budget vs. Bid Adjustment Decision)) are worth investigating.
"if you order by spend, you're going to find that usually most of your spend is going to be concentrated on your top five to 10 keywords."