Hello again Rex, could you take a look at this and check that it works correctly ?, I get the feeling that there are still some strange things.
There is a lilac sprite which is the area where the random points are set.
The red sprite sometimes leaves the area as if a point had been put beyond the zone and continues making some very abrupt movements, I do not know if this is a fault but I think so.
It may be necessary to run it twice or three to make it happen but in my tests most of the time it was seen in the first run.
https://www.dropbox.com/s/d922fgrd0sg05rf/testSpline.capx?dl=0