Hi Tony, getting back to your original point, even with the string trapped I believe that a hit on the kill would have still been evident.
When we hit the kill, the paddle moves backwards (before the faceplate) and in my example below its about 40mm paddle movement even before the faceplate starts to fall.
The paddle would move 20mm until it reached the point of 'no return' then a further 20mm before the faceplate started to fall backwards.
IMO if the string was tight and held by the tree bark, the target faceplate would still have tried to fall backwards as the faceplate is then being forced by a) the spring, and at this point b) the weight of the paddle, also helping it to fall.
On the particular shot that you have mentioned, as it was high up in the tree, the movement of a paddle hit should have been obvious due to the angle looking up, also a marshal inspecting the target would have seen the paddle fallen back even if the faceplate hadn't.
If you think you hit the kill but the faceplate hasn't fallen, always ask a marshal to check it, even if you do get a ribbing from fellow shooters, especially if Pete Dutton is in the next lane
After all its just part of the target shooting banter