Quite a few people in the UK have reported it, and there are also many reports of the fault on German, Dutch and French websites. It's not an isolated issue, but a design flaw in that motor.
Not many people are reporting reliability issues with Bosch motors, Yamaha or Panasonic. Kalkhoff bikes used to have Panasonic motors, before they decided to develop their own (I guess to keep their manufacturing costs down).
Unfortunately, in this case, expensive and made in Germany does not necessarily equate to more reliable. They probably made about 45% margin on the bike you purchased. A push version of the bike you bought (without motor assistance) would probably be worth £500-£600 maximum.
See
for example http://www.kalkhoff-bikes.com/de/bikes/my-bike/allround/agattu-hs-8r.html
Adding a mid-drive motor and battery would probably add £600 - £700 to the price, so you can guess their margins. You could create the same electric assisted bike, for about half the price (at retail cost).
They are fully aware of the issue (after pretending there was no issue for several months). Just ask them to commit in writing to provide you warranty on the motor for a reasonable duration/mileage (e.g. 4 years/6,000 miles, given the bike cost) and see their response, in term of how they stand by their products.
I don't think there is much they can check, as the motor is a non serviceable part. The main issue to check for is whether you start getting some noise from the motor, usually indicating an upcoming failure.