SortOrder Error "SortOrder must be in sequential order from 1" During Change Set Validation

To resolve this issue, perform one of the following actions depending on your situation:

1. When deploying reordered existing rules
Include all duplicate rules that have been reordered in the Outbound Change Set.

2. When deploying new rules created in the source organization

Set the order of the duplicate rule in the source organization to be the last among the existing rules in the target organization.
Alternatively, include all duplicate rules whose order was changed in the Outbound Change Set.

Note: All duplicate rules, even those that are inactive, must be included in the Outbound Change Set if they affect the sequential order.

For more information on ordering and reordering duplicate rules, please refer to the following Salesforce Help:

Customize Duplicate Rules