After merging two accounts in TA, the dupe account may not be deleted from CRM and have this sync error on the T2B delete:
This constituent is being deleted due to a merge in Team Approach, but some BBEC data has not yet been moved to the target constituent.
This error may occur when there are sync errors moving data from the dupe account to the retained account in CRM. Check the retained account for sync errors and resolve those. If there are a large number of sync errors and you want to just focus on the ones that are blocking the delete, contact TA support to identify which ones are from data on on the dupe account.