Cart items disappear on reload

It's 14:10. Your Rails monolith reads from a pool of three Postgres read replicas behind a load balancer. Support is paging: users report that items they just added to their cart 'disappear' on the next page load, and a few report seeing other people's stale data. The pg_stat_replication view shows replica-2 at 47 seconds of lag and climbing; replica-0 and replica-1 are under 1 second. Grafana shows replica-2's CPU pegged at 100% and disk write IOPS saturated. A bulk-import job that rewrites the products table was kicked off by the merchandising team at 13:55. Walk me through how you triage and mitigate this.