Importing new Leads following the reference Help topic Adding New Leads with Multiple Contacts via CSV Import (ID: 24587) creates duplicate Address on the new Lead record depending on the number of Contacts linked with the Lead
As per testing, this is how the Leads and Contacts CSV import is processed:
1. System will first create the Lead record
2. Then System will update the newly created Lead record and link the Contacts (steps will repeat depending on the number of contacts)
*During the update process where new Contact is linked, the Lead record is also updated and creates the new Address causing multiple entries
To prevent this from happening, the following setting should be configured during Import:
*Overwrite Sublists should be marked under Advanced Options
-As per field level Help for Overwrite Sublists: For updates, enable this option to cause imported sublist data to completely replace existing sublist data, instead of selectively updating or being appended. When this option is disabled, imported sublist data selectively updates keyed sublists and appends to non-keyed sublists.