A page can sit at position two for six months and still lose the job. The snippet above it becomes an overview. The people who used to click start getting the answer without a visit. Your rank tracker draws a flat line and calls it health.
Watch the click. Watch the session. Watch whether you are cited when someone asks the question in a chat. Then decide if the page still earns its keep — not whether the blue link is still in the same slot.
This is the same attribution problem as a core update, just quieter. Put the SERP change on the calendar anyway.