I can't replicate this. I can change the ordering of repeat groups by changing the list ordering. I seem to recall making a change quite some time ago that was overriding repeat group ordering, but iirc that was about a year ago.
If you want to enable Fabrik debug (Fabrik global options, debug tab) and point me at a form my 'fabrik' user can see, I'll take a look at what the query is doing.
Which list is that ordering on in post #3? I don't see that on this list (Travaux).
As I said in post #2, the ordering needs to be on the "main" list. We don't look at ordering on the list the repeat groups are based on. Only the main list.
When you do a list join, you aren't really joining to a Fabrik "List", you are join a list to a MySQL table. Note that in the dropdown for the table to join to, you are shown all the MySQL tables, not just ones you have Fabrik Lists for. You may have a List built on the table you are joining to, but none of it's settings are used for that join. It just becomes a part of the "main" list.