Interactive Diff Pair Length Tuning Altium Designer
Found a solution, and it's a little bit tricky...

If you do this :


And if you click in the position :

1) You get the Primitive not coupled error

2)&amp;3) It's working fine, but Altium is not modifying the 1)

The trick is that you have to do a "discontinuity" in the wire, like this :



In :

1) You get the Primitive not coupled error

2)&amp;3)&amp;4) It's working fine

It looks like Altium in Differential pairs is considering a direct wire from (in this case a via) like a pad or something...

Hope you found this use full.