It doesn’t matter what you see in a relation column. You are just trying to establish a link to related rows. If you see anything (question mark included), that mean it found a row.
You probably have multiple rows that can match. with the multiple checkbox unchecked, it just going to lock onto the first one. Not the last one. Your button is probably changing a previous record. Read this thread for a way around that. You could also use a query column in place of a relation to drill down deeper to the correct row you want.