Hmm, not familiar with either of the electronic systems you have tried but if they don’t use the standard cam to trigger then that blows one theory away. There have been instances of badly machined cams which can trigger at more than one point especially if the points gap is a tad small.
I had a similar problem with a TS150. I am not convinced I ever got to the bottom of it and it seemed to become more prevalent after I fitted a Velleman transitorised gizmo – which reatins the mechanical points.
two things I can suggest but try them one at time. Firstly retard the ignition to 2mm btdc and see how the engine behaves. It should reduce the kickback and probably will not have a huge effect on performance though there could of course be a risk of running hotter. If that works then at least you know a cause and may be able to reach a compromise on timing. The other thing to try is a faster idle speed. Slow steady idles are great but they would tend to facilitate engine reversal if the motor is prone to it. My TS150 would reverse whilst ticking over at traffic lights – keeping the speed up helped.
Best I can suggest. If you do ever solve the problem let everyone know how as it will add to MZ folklore.
Peter