Connect Dropdown filter on CMS (not showing duplicate records)

Hi

I have a CMS Collection which contains FirstName & Surname fields.

Some of the records e.g. people, have the same Surname, however when I use the "Connect Dropdown filter " connected to my Dataset via Surname it does not show the duplicate surname people.

E.g. Records in the CMS exist for …

Bob Smith
Eve Smith

But filter dropdown only shows one “Smith”

I’m using Wix Studio, any help would be appreciated, many thanks

regards
D.