I replicated your use case and I can’t get the sort to work, either. Maybe it’s a sorting bug related to groupings/aggregations? If nobody responds with a solution, it might be worth filing a bug report so Bubble can fix the bug or let us know what we are doing wrong.
After searching what I thought was everything before posting my question, I also saw that thread late last night and it certainly looks like exactly the same problem.
It looks like this bug has been sorted but now I have a seperate issue.
I want to export the grouped and sorted repeating group to a json file.
I have successfully done this using the Thing(s) to json plugin on other repeating groups but when I do it to this RG all I get is ‘null’ values for each row.