'This lead was already converted to the contact' error in Lightning Experience

Error Behavior in Lightning Experience

The error message appears in Salesforce Lightning Experience (SFX / one.app) when an Apex trigger converts a lead. After the lead is converted by the trigger, the Sales Path component attempts to reload the record. Because the record has been converted during the same save operation, the Sales Path component cannot load it and displays the "Error on loading Sales Path" message.

Why This Does Not Occur in Classic

The code path for lead conversion in Salesforce Classic is different from the code path used by Lightning Experience (one.app). This behavior only applies to the Lightning Experience interface. In Classic, the same trigger-based lead conversion completes without displaying this error.

Expected Behavior

This behavior is by design in Lightning Experience. The trigger-based lead conversion completes successfully — the lead is converted to the specified Account, Opportunity, or Contact as intended. The "Error on loading Sales Path" message is a display artifact from the Sales Path component attempting to load a record that has already been converted.

No further action is required. The lead conversion is successful. To confirm, navigate to the Contacts or Accounts object and verify that the converted records were created as expected.