The unit has an Over - Temperature Protection feature. 
After an extended time spent cooking, the electric board inside is at a higher temperature, in this high-temperature environment it is difficult to supply high power continuously, therefore, it needs a break from time to time and may pulsate.

When checking with the engineer he advised:

 1.  When the cooking zone uses 4 zones together, induction hob setting at high power level, after a long time cooking then its power will automatically be reduced as a safety feature. If you want its power to become higher, you should turn off the whole cooktop. And then turn on again.              
2.  When cooking with 1 or 2 zones, the heat/power will reduce after longer periods of use. You can increase the heat/power by selecting a new power level, adjust to 0 level and then increase to a new level of heat that you require. Or turn off and then turn on to restart the higher power.

Please note: Warranties do not cover maintenance, installation or user errors as per our Warranty T's & C's, fee's will be on-charged.