When you add an index in a view, depending on the dimensions on the rows and columns, and depending on the table computation, it may do some domain completion and add some marks.
As you can see in your case you go from 11 to 29 marks. So it will be difficult for you to use the index function for the sorting.
If the current and Next Marker have only a few values like in your example, then you can go with the alternate solution proposed in the attachment.
sort_crosstab2 ed mc.twbx 39.1 KB