When switching a business unit ' s Marketing Cloud Connect connection from a sandbox instance to a production Salesforce instance, the previously established integration artifacts — user mappings, profile attribute mappings, and tracking subscriptions — were built specifically against the sandbox org ' s user IDs, record structure, and configuration, and will not automatically and cleanly carry over or reconcile against the new production org ' s distinct identifiers and configuration. To avoid functional disruption (broken tracking sync, mismapped users, orphaned subscriptions), these existing sandbox-specific mappings and subscriptions must be manually removed and then rebuilt fresh against the newly connected production instance, ensuring the integration ' s configuration accurately reflects the org it is now actually connected to. Option A describes configuring for ' two production instances, ' which misstates the scenario — Cloud Kicks is disconnecting sandbox and connecting production within its own single business unit context, not managing two simultaneous production connections. Option C, updating query activities referencing synchronized data extensions, is a downstream consideration that may become necessary but is secondary to first properly resetting the core mapping and subscription configuration. Option D, renaming/deleting sandbox synchronized data extensions before connecting, is a more drastic and less precisely targeted action than the documented recommendation to clean up mappings and subscriptions specifically. Reference: Marketing Cloud Connect, Switching Connected Salesforce Instances.