Issue
When looking up a list with the List Lookup control on a Nintex Form and a Source View is specified only 30 items are shown in the control even though the Advanced section of the control settings specifies an item limit of 2000 by default.
Resolution
In SharePoint modify the List View that is specified as the Source View in the List Lookup control and go to Item Limit. Increase the limit to the desired setting.
Additional Information
When specifying a Source View in the List Lookup control the List View settings override the item limit specified in the advanced section of the List Lookup control.