This article describes sorting change order in 12.10 compared to 11.20
For example if you open the same app in 11.20 and 12.10 you will notice a change in the sorting and the sorting settings as well.
This has been considered as a WorksAsDesigned bug and below is the explanation from Rnd:
Sorting for charts that contain hidden columns will not be the same when opened in 12.10 as it were in earlier versions.
This is due to
QV-4966 which changed it so that the sort ordering between columns is kept not only for the currently visible columns.
The change was made to preserve sorting when hidden columns was involved. In earlier versions whenever you made a change that changed the number of columns in the chart it would reset the sorting to be on the first column. Now it should remember which column you sort on even if columns appear or disappear. The drawback is that if you consistently switch between 12.10 and earlier versions, the sorting will reset when you open the document in another version than it was saved in.
As long as you don't keep switching between 12.10 and earlier versions it should work fine. Once you have saved the document with the correct sort order in 12.10, it should work like before.