Auto-Generated Numbers might have been enabled at the time when the campaigns were created or IDs were created manually. By default, the Lead Source dropdown list is sourced from the Campaign IDs. If the Campaign ID field is empty, the Campaign Title will then be used.
- Navigate to Lists > Marketing > Marketing Campaigns
- Campaign: Click Edit
- ID: Remove ID
- Click Save
- Repeat steps 3 to 4 for each Campaign
Note: The solution considers that there would be no scripts or workflows that run on the Campaign records, preventing the ability to edit the ID field. Check if Campaign ID are essential to your business process before removing them.