I would suspect that the RAM is causing this problem. The memory you are using is not listed on the tested memory lists for yours NUC:
Take into consideration that your NUC supports DDR4 speed of 2133 MHz while you are using 2400 MHz.
I see this over and over. The KY NUC was not designed for nor validated to work with memory running faster than 2133MHz. There are two issues. First, whether particular memory will work is dependent upon the noise present in the circuit as well as the rate at which memory transfers must be latched. It may be possible that it will work initially but, as circuits age, noise only increases. Eventually - or perhaps immediately - the noise will exceed the threshold and transfers will fail. When they do, this can manifest as memory read/write errors (sometimes recoverable, sometimes not) or it can lock up the memory bus completely. If the latter occurs, the recovery watchdog will (eventually) reset the system (the system will appear to spontaneously reboot). The second issue is that running memory at any speeds above 2133MHz is technically overclocking at least a part of the processor. This can result in higher system temperatures (even at idle) and even more-volatile temperature changes.
Bottom line, I agree with Leon, testing with 2133MHz memory would be a prudent next-step. While it's true that this could be a red herring and have nothing to do with the actual issue, it is the thing that can most easily be tested...
Hope this help,