Ciao Mic 
The small and narrow 18" tyres are of course very sensitive regarding level differencies of the road in riding direction - what did you ride before the Strida?
But also, there is a certain reason existent which can make a Strida extremely twitchy:
That are damaged or broken bottom tube bearings (part nr 100-03 and 100-04);
you can check them easily yourself, they have to be visible present and intact.
It is definitely not required that they run perfectly and smooth (even brandnew ones don’t!).
With a few simple tricks is that truly doable, no worries 
(For a perfect result you should own a cable cutter plus a little bit of patience - just one hint.)
Hmmm…that is odd, there is just one bolt and you can’t mount it wrong I believe…
Does it fall always at the same side, left or right?
Cheers,
Chris