We have a category with page titles with incrementing numbers with 1 to 3 digits. As $wgCategoryCollation is set to uppercase by default, the page titles get sorted by the ASCII values of the chararacters instead of their numeric values. Thus, 100 comes before 20 etc. Setting the value to numeric would sort the titles correctly.

Please note that the MediaWiki manual tells to run updateCollation.php after changing the setting. I did not find a way to change the setting on ManageWiki.

Currently, we have worked around the issue by specifying custom sort keys for the page titles with only one digit, and recently, for titles with three digits as well. I think having numeric category collation would be cleaner so we would not have to keep adding the workaround for new pages.

For reference, I found an earlier task that asks for exactly the same configuration change: T6213