In order to determine if the issue is the processor of the motherboard, I would suggest testing the processor on a friend’s motherboard, or testing another processor on your system.
Make sure that the testing motherboard / processor as fully compatible.
I also have an issue with my i5-2500k, it runs at stock settings and I did a realtemp and Prime95 test to see what the temps would be (to check if the TIM and cpu cooler were applied correctly). And I keep getting that the worker in core 3 creates an error. Temps don't go above 54 celcius on 100% load. Should I be concerned?