How to read a core update without panicking
The instinct after a traffic drop is to change something immediately. This is usually wrong, because the most common cause of a second drop is a panicked response to the first one.
Confirm the timing before the diagnosis
Compare the drop date against the confirmed rollout window. Rollouts take one to three weeks and traffic often moves twice within them, so a decline that started before the rollout began is not the update.
Check whether the drop is site-wide or confined to a section. A section-level drop points at a content or intent problem. A site-wide drop points at something structural or at a genuine quality reassessment.
Separate ranking loss from SERP change
Traffic can fall while rankings are unchanged, because the shape of the results page changed. More ads, a new feature, an expanded answer box, or a shift in what page type is being rewarded will all reduce clicks at a constant position.
Search Console impressions and average position will tell you which happened. If impressions held and clicks fell, you have a SERP problem, not a ranking problem, and the fix is entirely different.
Wait, then act narrowly
Wait until the rollout is confirmed complete before drawing conclusions. Then pick the single most affected section and work out what the results now ranking above you are doing differently.
Resist site-wide changes. The pages that did not drop are evidence about what is working, and a site-wide response destroys that evidence.