2016 zafira tourer 1.6 cdti cam sensor (p0340/p0341)

ive recently had my engine (b16dth) replaced and within 3 days of it being back up and running i get the error code P0340, when this code is present the car will not start if switched off. However, if left for a few hours the vehicle will miracuously start up like nothing has happened. all the usual things have been checked. the engine has only covered 25k miles, has anyone every had any issues like this? this is an intermittent fault which comes and goes throughout the day. if more details are needed please say as im new to this.

thanks