The sensor movement test is supposed to be started when your CPU is idle.
Intel's temperature sensors were designed and calibrated to control thermal throttling and thermal shut down. 100% accurate core temperatures from idle to full load were never part of the design goal.
Most of these CPUs have 1 core that is significantly different than the others. It might be a bad sensors or it might be the way Intel calibrates their CPUs or it might be the way Intel attaches the IHS to the CPU cores. No one knows and it doesn't matter. As long as your CPU runs reliably without throttling then there is no reason to be concerned about the core temperature.