Don’t think Roger has seen this post but I can answer it on his behalf as he gave me the Vape unit to investigate after he converted his bike back to 6v electrics.
The cdi unit itself worked fine under test on one of my other bikes. The problem turned out to be the charging coil on the alternator, which is one of the earlier type with an external trigger coil.
Eventually it failed completely. There were clear signs of corrosion on the whole unit and as the bike was used for MCC type trials and green laneing, I suspect it had been soaked a few times which will not have helped the very fine windings.
You can buy a replacement stator unit from Vape but its near £90 before you get into the complexities of importing from the EU these days. As an alternative, I converted the unit to a DC cdi system with separate conventional coil and using the original trigger. It works on the bench and the timing seems to be about right. Covid-19 restrictions and the cold weather have prevented a road test but I am hopeful it will work, if so the cost was about £13 for a Chinese made cdi unit.
The drawback is of course you need a battery as it is no longer a self energising system, but the 12v charging side continues to work fine, the windings on the stator for this are far more robust.
Helped to pass the time during lockdown.