Your prefill is not working because you have multiple records with the same value in the primary field. In this situation, Airtable cannot tell which of the four records you want to link to, so it does not link to any of them.
Solution 1: Change your primary field values so that every record is unique.
Solution 2: Prefill using the record id of the desired record, instead of the primary field value.
Update: it does work, but only sometimes as long as you are testing it in the same browser where you do the designing (Edge in my case). When I use the exact same link in a different browser where I'm not logged in it works fine.
Maybe a strange buffering / record caching issue? Or an Edge thing?
@Tuur is correct. If using the link in a separate browser from the designing browser, it works fine. So the form prefill works for your users, but not you (at least initially). I have tested it with other users and the form prefill works fine for linked records.
