Does you CPU go to 100% when you do not build lightmass and use the engine for something else? 10700k is a very capable chip.
Even so, the processor and its cooling should be able to handle 100% load for 24h without overheating. Games are generally not that demanding, but the tools used to make those will take everything you throw at them, be slow and ask for more resources.
What cooler is on the CPU? Perhaps it’s a matter of cleaning it.