Below is a copy & paste reply that AkaPete gave in another thread. My opinion now is that Wahoo added cadence to Kickr Core as a distant second to power measurement. The sensors or algorithm is not precise enough to give the accuracy desired.
As you’ve surmised, the KICKR doesn’t measure cadence directly. Instead, it analyzes the pattern of your power over time. It assumes that power will be lowest when the pedals are in the 12 o’clock/6 o’clock positions. By measuring the time between low points, it can estimate your cadence.