Hi all,
After lots of trial and error, I found a way to sort a repeating group that uses :grouped by!
What you have to do essentially is create your repeating group normally like you have been, and use the :grouped by like normal. However, in each cell of your repeating group, you need to add another group. You can then set this group to be the elements you need by using the repeating group as a list of data, and matching it against search results, using the cell index to create the new list.
Since this is very confusing, here’s a screenshot of how I set up that group that’s in each repeating group cell (group on the right, search being run on the left):
I can now sort by any field for my data types! Hope this helps 