Thank you for submitting this idea, we are currently reviewing it and we would greatly appreciate if you could provide us with more examples and use cases to show the need in secondary sort.Bettina Kaldenberg commented
After some thought and discussion I am not clear if sort by relevancy as the first sorting criterium is the correct starting point. Since relevancy is built on a range of internal decisions, it is not likely that many records will have the exact same relevancy rating. Sorting them then according to a secondary sort criterium is not going to be much help.
On the other hand I can see the use case where for example a student wants to get an overview about the text book collection and sorts the list by publication year. Then 2018, 2017 etc. is going to be sorted internally by relevancy, where in this case a sort by author or title would make more sense.
Now, does this reasoning make sense to others? Or can you provide a use case (maybe even pointing to your library's Primo) where first sorting relevancy / second sorting anything else can be demonstrated more clearly?