The first revision
A popular cache entry expires during a traffic peak. Requests arrive together, all miss, and all ask the origin for the same result. The database sees a sudden jump even though product demand did not change.
Why it gets worse
The initial miss is not expensive by itself. The synchronized fan out is. If the origin slows, requests wait longer and occupy more application capacity.
Repair options
Coalesce duplicate work so one request refreshes the value. Add random variation to expiration times. Or serve a stale value while a background refresh happens. Each repair changes freshness and complexity.
Replay
Raise traffic, expire the hot key, then enable request coalescing. Compare origin requests and cache freshness rather than looking only at average latency.