Custom Sort not working

I have a database with surname, christian name and other colums of data. There is a header and I have included the header when custom sorting the data. the data is sorted surname and christian name and no other columns. I have highlighted all colums and data and asked it to custom sort by surname and then christian name. Unfortunately no matter how many times I try there are a number of the same surname and different christian names and the christian names are not sorting alphabetically A - Z Any help?

I had tried this but it still does not work. There is only one name that has not sorted out of all the data

I have manually re-entered the whole line and deleted the original and asked it to sort and it has worked or at least it has not moved the new line. As suspected there was probably a hidden gremlin. Thank you for your assistance