The number of times a Custom List appears on the Use Existing List dropdown in Step 2 Create Item Property List in Matrix Item Assistant depends on the number of Item custom fields which use the same Matrix Option Custom List.
- Navigate to Customization > List, Records, & Fields > Item Fields
- Show Inactive: Enter Checkmark
- List column: Take note of the Item Fields which use the same Custom List
- Inactive column: Enter Checkmark for the Item Fields that are not used
- Click Submit