Probably 90 percent of the time when I playback a script the outcome is as expected, however there is the odd moment when things don't quite work out so well.
In these cases I generally solve any issues by figuring out roughly which line number the playback has a problem with which can take a bit of time by trial and error, involving chopping around with the arscript file in a text editor and rerunning.
So an idea that I have is to add a toggle button (defaulting to off) on the initial play script replay popup dialog that when enabled displays the arscript line number that is currently being executed during playback. So that when a deviation from the original drawing is spotted during playback the line number is visible allowing the inspection of the arscript at exactly the correct location for any issues that can be addressed.