I think I may have figured it out (only tested once). Before, the units would continue along the route unless you added an advanced waypoint action “disperse under fire”. Now, they seem to disperse even without the action selected. It is tricky an not intuitive, but what you need to do is add the action “disperse under fire” (even though they already do this now by default). Next, look in the details of that action and there is a checkbox to disable it.
So yes, you need to add an action and disable it at the same time.
If you had a mission where units would continue along the route and not disperse under fire, I suggest you check out your mission again since something seems to have changed in one of the more recent DCS updates.
Cheers guys.