You have a List Content Type with a Lookup Field for which you cannot set additional lookup fields from the User Interface.
You can use Powershell (server side) to set the additional lookup fields by explicitely adding a field link object to the target list content type.
| # Get the target list content type | |
| $ListCTs = $targetsite.Lists["targetlisttitle"].ContentTypes | |
| # assuming the content type is the first one | |
| $ListCTs[0].FieldLinks | ft DisplayName | |
| # This displays the current fields included in content type, you may note some difference from what can be seen in the UI. | |
| # search for the field you want to include in the list content type | |
| $targetsite.Fields | ? { $_.Title -match "yourmatch" } | |
| # create a field link | |
| $TargetField = $targetsite.Fields["targetfieldtitle"] | |
| $TargetFieldLink = new-object Microsoft.SharePoint.SPFieldLink $TargetFieldLink | |
| $ListCTs[0].FieldLinks.Add($TargetFieldLink) | |
| $ListCTs[0].Update() | |
| # check the field link has been added | |
| $ListCTs[0].FieldLinks | ft DisplayName |
