I get this error at least 3/4 of the times I've tried to print over the last few months. It usually takes 3-4 tries to get it to pass the core height check.
The problem occurs during the first test it does (for core 2). It doesn't even try. It should take about 10 seconds for the bed to reach the nozzle (it does for the second check, for core 1), but instead it stops after just 1-2 seconds, when the bed is nowhere near the nozzle. Then it checks core 1, then the error. The nozzle and bed are clean.
It's very frustrating, especially because I'm usually only using one core, so height difference between the cores is irrelevant. I wish this test could be turned off.