I gave your scen a try, and everything seems to work as designed.
If you change a change a patrol zone after the assigned units have plotted a course to the PZ, they will fly to the endpoint of their plotted course,
and then plot a new course to the PZ. If you select a unit and press F3 and then escape, the old course will be deleted and a new course to the PZ will be plotted.
This is also why the A/C seemingly won´t attack the target. If you let them fly to the end point, they will plot a new attack course and engage the target.
All the ref points are set to rotating relative to the convoy. Try turning the convoy, and you will see them follow the plotted course.
The ships are cavitating at 10 knots, because cavitation is caused by low pressure bubbles collapsing in the wake of the propeller blades. The higher the ambient pressure is,
the later the onset of cavitation. This is why subs dive deep when they run fast. Surface ships don´t have that luxury, so cavitation starts at low speed. in this case 8 knots.
Regarding your picture. I believe what you see there is also caused by you changing the ref points of the PZ after the A/C have launched, but without a save game I can´t be sure.
Hope this helped.