So if you select them an use the Flip Reference Line command, nothing happens?
Flip wall on reference line works. However, I notice that if I change the reference line in the ordinary menu/info box palette or retroactively try to change the reference line through the same menu, my choice doesn't "go through", i.e nothing happens. Although, if I change the reference line through Edit>Reference line and plane>Modify wall reference line, it works! However, this would be very time consuming in the long run ofc.
Does this happen with all of your walls? Might it just be your Reference Line Offset?
Yes, all walls in this particular file. No reference line offset.
It would be more informative if you selected your walls in question in your screenshot and possibly use a Composite Wall so that it is easily visible which side is which.
See screenshot below
Archicad 19 | Windows 10 Home | Intel(R) Core(TM) i7-4710HQ CPU @ 2.50GHz | 16 GB RAM