I can't say I'm all that happy about abandoning the original circuit but I must admit that with a 3 stage RC filter 3 x 10k/0.0068uF the trigger pulse looks much cleaner and triggering more stable and interlaced.
https://youtu.be/JzJ4Lik8R90
Excuse the poor resolution and aliasing in the Youtube:
https://youtu.be/Lgz08qIv20c
Peter