Hello,

The built-in autocomplete/ filtering mechanism relies on the field names of the columns in the underlying grid. The property name of an applied filter descriptor needs to match the FieldName property of an existing column in the grid. The data is filtered by the field specified as DisplayMember. This requires binding the control:
https://docs.telerik.com/devtools/winforms/controls/multicolumncombobox/populating-with-data/databinding

I hope this information helps. If you need any further assistance please don't hesitate to contact me. 

Happy holidays 

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik