APNX-3-1000-030 Record Sync Failure

v21.4 Cloud

I am getting the below error when updating data of a synced record using a process that has Write to Data Store Entity nodes and Write to Multiple Data Store Entities nodes.

[Appian Work Item - 773428 - execution02 : UnattendedJavaActivityRequest] ERROR com.appiancorp.record.service.RecordReplicaUpdateService - Loading updates to synced record type(s) in ADS failed, invalidated record type(s): [(da0a35ad-c98f-40e7-975c-47ff016a2084,WMS Request)]
com.appiancorp.suiteapi.common.exceptions.AppianException: Unable to sync due to a system failure. Issue identifier: [8d98eb66-d7a7-4786-b881-d48850c684cb] (APNX-1-4521-016)

...
com.appian.data.client.AdsUserInputException: APNX-3-1000-030: Invalid transaction data. Cannot update the same entity multiple times in the same transaction. Invalid id(s): (100218067)

This error is not covered in the docs so unable to find guidance on how to resolve it - docs.appian.com/suite/help/21.4/Records_Monitoring_Details.html#other-sync-errors

Has anyone run into this error? What does "Cannot update the same entity multiple times in the same transaction" mean? I should be able to write or update the Request record how many ever times I want in the process. 

Here is a short desc of the data model and the process that updates the synced record:

• The data model has 2 synced records - Request and Task - 1:N relationship. The relationship has been setup on both the records
• The creation process model of the Request record works fine and both records are immediately synced after the are written to the db
• The update process model however causes the immediate sync to fail. The data is updated correctly in the db, no process errors but when I try to open the record I see the record sync failure error message.
• The monitoring page for the sync shows that the sync failed (which means the immediate sync) during a "Write to Source" event - 

  Unable to sync due to a system failure. Issue identifier: [1e56f60d-f25a-43fe-bb1b-c2e9861abd60]

  Process Name: <ABC>
  Modified Source Rows By Primary Key: 49