Yesterday you observed: the number of users switching accounts increased, while overall active users decreased. Propose a concrete diagnostic plan. Include: (a) 5–7 plausible hypotheses spanning measurement artifacts (e.g., deduping by person_id vs user_id, SSO changes), product changes (friction in login/logout, session expiration), and behavior shifts (multi-account consolidation, spam mitigation); (b) the exact metrics and breakdowns you’ll pull (by client, geo, new vs returning, person_id vs user_id, cohorts, time-of-day); (c) at least three targeted slice analyses to confirm or refute cross-contamination between accounts; (d) event/experiment diffing to identify recent launches correlated with the shift; (e) a minimal SQL or pseudocode outline to quantify how many active user_ids map to the same person_id compared with last week; and (f) the immediate mitigations you’d try if the root cause is (i) a logging bug, (ii) authentication friction, or (iii) users gaming policy limits by rotating accounts.