When viewing a list a reference field which should have a value shows '(empty)' 

This may only be seen with a specific number of columns on the list, and you may not see the issue if you remove some. 

Another field in the list has a bad reference to either an orphaned record or a sys_id that does not exist on that table. This causes it to not have a display value and then the other field which should have a display value also shows as empty.

Remove the incorrect reference data from any reference fields on that table.