After moving from a single-region to a multi-region active-active deployment, the team starts seeing intermittent data inconsistencies between regions for a service that wasn't redesigned for this change.

This usually indicates the service or its database wasn't actually built for multi-region writes — if both regions are accepting writes to a database that isn't properly multi-master/conflict-resolved, simultaneous writes to the same record in different regions can produce inconsistency. The fix requires either redesigning the data layer for proper multi-region consistency (conflict resolution strategy, or routing all writes to one primary region with read replicas elsewhere) rather than simply replicating the existing single-region architecture across regions.