Outbound Campaign Sync Error 409 with Legal Hold Metadata

Ran into a weird issue today with the outbound dialing API when syncing contacts tagged for legal hold.

Error 409: Conflict - Metadata Mismatch

The export job pushes metadata to S3 correctly, but the outbound campaign sync fails when trying to update contact attributes for these specific records. Genesys Cloud London region, v3.5.2. Is there a lock on records with active legal hold flags preventing outbound attribute updates?