I noticed in your previous code, you had specified "ascending" in the "Sort-Object" flags. An ascending sort is the default, and cannot be specified by flag. To sort in descending order, please make sure that "-descending" flag includes the "-" at the beginning of the word.
Below are 3 PS snippets that offer different sorted output.
#Provides a list of LUNs sorted by LunID in ascending order without respect to the igroup name