If you Query or Lookup a HubSpot Deal using an ID from one of the merged Deals, such as Deal A in our example, HubSpot locates and returns the new merged Deal, Deal C.  

However, if you need to get associated records based on a Deal ID and the Deal ID is not found because it is from a merged Deal, HubSpot does not return any records.  For example, if you request associated Contacts for Deal A, no records are returned.  

To work around this issue, use a Lookup or Fetch Block with the old Deal ID as matching criteria to locate the new Deal ID.  Use the new Deal ID to request the associated records. 

Note: If you are using HubSpot Deal IDs as external IDs in another system, such as a CRM system, and your Maps use those IDs to work with associated records, best practice is to create a Map that updates the external IDs with the new merged Deal IDs before using the IDs to synchronize HubSpot and the CRM system.

See the Deals now support merging HubSpot announcement for more information.