When you say a New Build when did you fire it up for the first time?
Have you run a Memory tester on it like Memtest86?
Are you Over Clocking the CPU and if so to what level? Slow it down and test.
Sure sound like a memory problem or if you are overclocking the CPU you don't have enough cooling or you need to slow it down some.
I was running a 3 year old 2.8Ghz i5 overclocked to 3.8 and the system ran fine for those 3 years. I was trying some new things in Photoshop CC and every time I click on one option the system would crash, system never crashed before in those 3 year. I slowed the CPU down to 3.6 and didn't get any more crashes.
So your problem is Hardware and not Lightroom.
CPU overclocked to much and or not enough cooling.
RAM bad/defective or if it is overclocked with the CPU overclocking it just can take it on memory intensive operations.
Faulty power supply. PSU can't deliver the proper voltages when call on when doing CPU and memory intensive operations.