Hmmm. I have to agree with mechanical logic here... If the misfire clears after just 30 seconds it isn't the injectors at fault.
Intermittent and erratic misfire would suggest injector in need of cleaning but not a straight from starting up and on a regular time frame and pattern.
It would rather suggest to me that it is a fuel pressure build up fault.
You are aware that the Jts has an under body fuel filter where the other ts and busso petrol models don't ?
A dirty or slightly blocked fuel filter that clears the sediment under pressure build up after starting.... Once the engine stops, the sediment settles again and thus the blockage returns ready for the next stat up.... It fits the profile of your fault.
I could be wrong but worth investigation further.
It's where I would start looking first before spending a fortune on sonic injection cleaning... If Terraclean didn't do the job it stands to reason that the injection system isn't at fault.
It also adds weight to a fuel line partial blockage as terraclean is fed into the fuel rail bypassing the fuel feed system and not via the fuel tank,fuel pump, filter and the normal fuel lines.
Have a look mate... sometimes we look at the over complicated picture and don't see the wood for the trees when walking face first into a tree trunk
It's located at the rear floor of the car near the fuel tank. It's a metal cylinder with one line in, one line out. A serviceable replacement item for around the £12 mark and often gets neglected even by indie's who are used to working on twin sparks which don't have them so if yours is in a bit of a state, chances are it will not have been changed for a long, long time if not never.
It's on a low pressure system so before changing, clamp the fuel lines and open the fuel filler cap to relieve the pressure before removing