You may have a CPU core that has a higher temperature than the other cores. With about 5 to 10 degrees more.
In fact according to the CPUs, the core 1 may have a higher turbo frequency than the others. This is a basic configuration. You can check this by going into the bios at the individual turbo settings of each core.
Core 1 is going to be the core that will work on most of the tasks that will be delegated to other cores when there is too much of them.
It is also possible that the thermal paste does not cover enough the surface of the processor and this one therefore sees its temperature increase.
You can close all applications and Windows tasks at startup and see if the temperature gap persists. If this is the case, there is a concern with thermal paste.
Use isopropyl alcohol (computer off and unplugged) in very fine amount on the CPU before applying the thermal paste.